Neuroticism is one of the Big Five higher-order personality traits in the study of psychology.

With the way he was scratching his left arm and right shoulder, seemingly keeping himself in an weird embrace, it was obvious how nervous the boy was. The big, emerald eyes darting from one person to the wall, to the bookshelf and to another person were as confused as they could be, and it was all because it was his first day in the middle school. He admittedly never had many friends- he was quirkless after all –and it was getting harder these days to make newly met people his acquaintances, but his resolve was shining brighter than the daylight. Never so quick to falter, he really wanted to have someone to talk to including one of those days when his mood would abruptly change; when he was feeling like he disappointed her mother; when his nightmares just didn't stop, only started to worsen; when he was so damn sure he got in a hole so deep down that there's been no sunlight since the Earth's beginnings. He's wanted a companion. A reliable person.
This was an entirely new beginning and, boy, he had no intention on messing it now.
Fate hate him, though. He knew.
Lost in thoughts, Izuku never noticed the on-coming person whose smirk grew right on his once frowning face. Said person, the taller blonde with eyes so red, like the hellfires erupting in them and spraying blood in every corner, like never-ending hatred and rage, like... like a bully, finally caught up to shorter boy and promptly grabbed a handful of strands of his rather long (past shoulder-length), dark green hair and pulled. Hard.
Izuku cried out when he felt his hair being pulled on and glistening tears gathered on the small corners of his big eyes, when some of the strands' been pulled out of his scalp.
It hurt.
"Long time no see, you fucking Deku!", said his oppressor and Izuku, immediately recognizing that voice, will-stopped the tears from leaking out. Trying to turn slightly in order to see his... friend, the boy caught the look Katsuki was giving him. Big, emerald orbs were wide in confusion and one could take notice of hurting which came with them.
But Bakugou didn't care. He never did.
"Now, why won't you answer me, useless? Or are you scared?" Fake worry etching into his voice wasn't reassuring, now Midoriya was feeling even worse, he couldn't do anything right, could he? Not wanting to upset childhood acquaintance any more than he already have done, the green-haired boy bit back the scream of pain when he felt his head skin coming off...
"Because you should be damn afraid of me," whispered Bakugou in a hushed tone like he was telling him a dirty secret of his. Izuku's eyes suddenly widened and tried to wriggle out of his friend's grip. No could have done.
Katsuki's cackling only grew, whenever he pulled on Midoriya's hair harder. This... this loser tried resisting, which succeeded in nothing.
He was shaking in an unspoken rage directed at the cowering boy beneath him. Fixated on making him pay, blonde had more reasons to scoop the smaller body up and clench his hand tightly on his arms.
"K-Kacchan!" exclaimed Izuku, coming face to face with his once childhood friend, now turned something entirely else. Midoriya quickly broke the eye contact, getting more off and anxious, redirecting his gaze at the ground under his sneakers. His eyes were flashing with emotions, the lone tear finally coming down his face.
But Bakugou wouldn't have it his way. He didn't notice.
"Why are you here, stupid trash?! You mean nothing, so why bother?" And his words were beyond hurtful.
Experiencing sudden and unexpected change in his mood (it was getting more and more often, he solemnly noticed), Deku grew irritated and shook Kacchan's hand off his body and took a shaky step back. What... what was happening with him? He never was the one to anger, patience so high that he could've put up with six Bakugous, but this... this was crossing his own boundaries. He stood up to Kacchan. Realizing what had happened just now, Izuku tripped and fell on his butt. By that time, everyone around them was watching the scene with unhidden curiosity. His head went up, but dread creeped on his back.
Wide eyes of Bakugou were the only thing he saw before his friend's brows furrowed. He snapped. And everything was covered in blinding white.

Individuals who score high on neuroticism are more likely than average to be moody and to experience such feelings as anxiety, worry,

He was rubbing his hands against each other ferociously, like he was applying a cream perhaps, but without the needed substance. It's been going along for almost an hour, since his meeting with the most unexpected person he could think of, his idol, All Might- or should he say Toshinori-san? It was the second day of getting rid of all the trash on the beach and who greeted him was certainly not tall, muscular man, but a sickly pale and skeleton-built guy. His true form, Yagi Toshinori.
And Izuku still adored every, every part of him, the one that he shows the world and the one he keeps only to himself (the one filled with endless void, loneliness, existential conflict and nightmare, because sooner or later they all become broken, lost in what-ifs, countless scenarios and panic attack, life o a hero ISN'T THE ONE THAT SHOULD BE UNDERESTIMATED, SOONER OR LATER ALL OF THEM WILL REALIZE THE DANGERS tHaT lIe AhEaD, BUT it will be too late for that.) Izuku not even once stopped believing in his hero.
All Might's words still clearly as hell repeated themselves again and again to the point where Midoriya's concentration and focus was greatly disturbed and disrupted.
[it's not bad to dream, but you also have to consider what's realistic]
And then he threw a bombshell on his mind. He was a real hero material. If he trained himself to the unconsciousness, passed the limits and boundaries his weak body had and became more aware of his surroundings, One for All will be passed on to him.
Never once he stopped rubbing his hands, even when his dried skin opened up and blood came out. Never once when his nails all's been broken, never once when these hands of his were so warm it was agonizing.
"What...w-what if it won't be enough?", he asked out loud, suddenly coming to his senses and noticing he was sitting tense on the edge of his white, comfortable bed in his All Might(and heroes)-centered room. Reddening hands slid off his knees onto the covers and immediately stained white cushions with red-colored, dense liquid. His breath caught at the sight of calloused hands, broken fingernails and veins sticking out very noticeably. He stared and stared, and all he did was stare.
He couldn't breathe. Impossibility to take any gulp of air, polluted or fresh, was frightening and his mind immediately, like on autopilot, went into "the panic mode" which hadn't seen the sun's rays since... since that one moment in the classroom... w-where... Kacchan and o-others...
He didn't realized that the door was being slammed open until a loud bang echoed through his room. Midoriya didn't move and inch, though. Sheets were already darkened, and the edge of his bed almost got a crack from boy's squeezing grip. Not until he felt his mother's gentle touch and soft, warm hand did he snapped out of this frustrating daze; but he still couldn't breathe. Midoriya Inko's scared and worried eyes informed him of what a shitty son he was – panic attack? Hyperventilation? Anxiety?
What the fuck was wrong with him?
He was a disappointment, a big one. His lips formed a tight line, getting bluer with every second, his complexion going from whit-pale to purple.
He still had to drew a breath.
But he didn't know if that's what he wanted.

fear, anger, frustration,

It was the day of the Entrance Exam.
And Izuku was 99 per cent sure there was something bound to happen, be it before or after that ultimate courage test. He had barely got any sleep that night, various scenarios playing somewhere in the background of his mind, whereas the main show (he barely contained the vision of himself going into another panicking state) was mainly on the display, his eyes bloodshot and wide, his hand curled, knees up and whole form trembling. But his bed was warm. It was his soul that was cold.
Getting up at first seemed to be a hard feat, but he did it relatively neutral – it was cold, cold world and no bed, no house and warmth was going to HEAT THE COLDEST DARKNESS OF HIS HEART aNd MiNd -
He sucked in a sharp, shaggy breath, breaking the cycle of ifs and whats mixed with dark thoughts. His mother's voice called him from down the house, announcing the breakfast. Izuku frantically shook his head, hair tangling and covering his eyes. He sighed deeply, thinking it was going to be a long, long day.
And he was mistaken.
Or wasn't he?
As soon as he could, he left the house, because no one could've stood their mother's disappointed face, guilty look and lips clenched in a tight line, which was a clear sign of a disapproval and negative feelings. In spite of being a nervous wreck almost the whole time, Izuku managed to pretty well read the body language. He had to- it was a must for him, if he wanted to survive the oncoming school years. He had the intentions of others read before they decided to open their mouths. He knew.
But he never admitted it.
Going out early resulted in him stepping into the bakery, the words of his mother freshly burnt in his mind. He grabbed a roll and paid for it, hands shaking, fingers curling and uncurling without a pattern, eyes narrow and hair messed up.
"You've got an invitation from Zurugashikoi High. Do you really want to refuse this chance?"
Damn she knew he wanted.
Zurugashikoi was considered to be the best school in the entire country. It's programme of teaching included university material and above it too. In addition to being located around 400km from his home city, students, who were doing the best among over three hundred pupils, were always sent to America, where the technology and science was even more advanced. It was a chance of a lifetime, but also the most stressful one and it could be easily missed. If he won't make up his mind till the Friday, the invitation will pass onto another person.
In all its greatness, Zurugashikoi wasn't appealing in one bit to him. He was dead set on becoming the greatest hero ever existing and taking the mantle of Symbol of Peace. Nothing could've changed his decision.
But his mother's words were repeating themselves again and again, without a break, they were plaguing his mind the whole way to Yuuei High. They did disappear when he spotted an angry Bakugou, glaring at everyone around him, chest puffed, head high and hands in pockets in all his cockine...-glory. His expression rarely changed and today was no exception. Although this day should have been chock-full with restlessness, Bakugou held himself firm.
Well, until something dark green caught his eye again. His red-eyed gaze slid down and met another, tired gaze of emerald eyes, shining with loneliness, contemplation and, surprisingly, drive. They were frustrating and getting in Katsuki's way every time. They-they were so fucking annoying that he just wants to STRANGLE THE BOY SO HE KNOWS HIS FUCKING PLACE, USELESS PIECE OF SHIT...!
Someone passed by, obscuring his view of Deku and when said person moved, Midoriya was nowhere to be seen.
Goddamn him. He's going to choke him later on.
Meantime, Midoriya flushed furiously, realizing that he was falling with an 'extreme' speed, straight on the cemented ground. The girl that passed by him unintentionally tripped him and he couldn't stabilize himself in time to straighten out and retain his fricking balance.
Wasn't accidentally falling something like a symbol of bad luck and clumsiness? Oh well, he was a perfect example of that.
And then, when he thought he had hit the bottom in every sense, he felt the delicate touch of a presumably girl's hand and literally floated.
Was it her quirk? Most likely. His eyes went wide and when he looked up, a friendly smile of a beautiful teenager greeted him. She was shining with happiness and optimistic attitude. Midoriya was nearly entranced; she was just pure.
"Are you alright? Sorry for going crazy with my quirk there," she brightly chirped, hands, which were touching his back, clasping with a dull sound. Izuku coughed, a little embarrassed, but thankful no less. "I just think it'd be a bad omen if you tripped, you know?"
She made a contact with him once again and he could finally stand. Standing straight, he turned his head in her direction and bowed a little.
"T-Thank y-y-you. I'm really grateful," he stuttered, screaming volumes in his head. Why he had to be like this? Why was he tripping but on his words? He was stupid –no one will deny this –and not until recently quirkless and antisocial and many things...
"No problem! I'm so nervous, bet you are too!" she threw and waved her hand, "Well, good luck and see you around!"
With that sentence, she ran into the crowd of wannabe heroes, disappearing behind the big, bulky man. Midoriya stayed in this place for a while, staring seemingly into the nothingness and then blinked slowly.
He... talked to somebody?
He was stuttering. Useless, unable to socialize, fucking mess. Why? Why he had to be like this?!
He didn't know and wouldn't know until the second portion of the entrance exam.
Zero points. That was his actual count, despite starting with a "start" and going ahead of everyone. His newly acquired quirk had yet to show up or he would mess everything up and disappoint not only his mother, but his lifelong mentor and new teacher too. He didn't want that.
Clenching his fist, he rushed forward only to stop when he heard a long, high-pitched scream from the opposite direction; someone was in danger.
His body moved on its own. Seeing that cute girl from before crushed under that building's debris awakened something deep, deep inside him. It was a call – the scream, that's it. With scrunched eyebrows, gritted teeth and hair standing up from the back of his body, his frustration and anger at no one but himself spilled out finally.
Something was flowing through his veins. His body tensed, when lightning bolts danced and spread across his whole form.
He felt that power.
Not really thinking (his body moved on its own, after all) he jumped up high, coming tête-à-tête with the biggest Zero point robot in this section. Then, he just punched, thinking about all negative feelings he had ever experienced.
The robot crumbled.
So did his legs. [But he was happy, he saved that girl, he saved someone finally].

envy, jealousy,

Izuku used to look at almost everyone with envy. After all, he hadn't had a quirk and was a little, fragile, stressed out four-year-old, who was already dealing with bullies and hardships of his relatively short life. It was a time where he developed his imagination to the point where he would see catastrophic situations and scenarios, but he was the hero rescuing people. He had an amazing quirk! (Once it was a telekinesis, another was it creating portals, and another was teleporting from really far place to other far city.) He was so cool, running around and helping everyone.
But dreams are dreams. He didn't have that possibility to become hero, to relax with his peers, to be himself.
He was something akin to ghost. A shell maybe? He wasn't his true self.
Just looking at Bakugou's squad made his heart pound a little, the pang making itself noticeable. Bakugou had so many friends whereas he... he didn't. Kacchan had everything. He had nothing.

guilt,

"Mom, where is daddy?" asked Izuku one time, when he was helping her prepare the dinner in their small kitchen. Inko's hand suddenly froze as her head turned in her son's direction. Her mouth formed a circle and her eyes narrowed. A wrinkle formed on her forehead.
"Mom? Is...is something wrong?" Her lips tightened with that question and she turned to the counter, cutting the vegetables. She didn't say anything for the rest of the evening and young boy had never felt so guilty and oh wrong at the same time. ...w-what? What caused that? His mother's empty gaze? Lips sealed shut? That despiteful dullness in green orbs?
He never talked to her about his father ever again.
Another time the feeling of wrongness and his fault appeared while he was training and it was a practical course that was held in order to judge the strength of Class 1-A. They split it into a few categories and with that Midoriya was supposed to be their trump card at the strength test.
Oh, how he failed and failed miserably. His arm had been broken in the outcome and his whole class, save for ever-sweet Ochako and ever-cool Shouto was glaring daggers at him throughout the following week. He didn't do great and that was the problem. He lowered the class' overall grade and never felt more guilty and at fault than then. His anger at himself had arisen before the Ochako's words of "It doesn't matter!" lightened his mood up. She always knew what to say, it seemed.
And Todoroki wasn't far behind her. He shrugged his shoulders casually and yawned.
"Who cares about it. Everyone have better and worse days, it wasn't your fault," he said, offering an open can of soda. Izuku opened his palm and had a smell of sugary drink. Then, he took a small sip.
He still felt guilty.

depressed mood, and loneliness.

There was a time, when their middle school homeroom teacher declared that he wanted to know about their plans for the future, precisely where they were going to apply. He ordered them to write t on a white sheet of paper and turn in to him whenever they are ready. Izuku gave it as the last of his class, "Yuuei High" being scribbled down on his sheet. The class was acting loudly, so turning them out, he grabbed his notebook and began to analyze some most recent pro hero's behavior – Mt. Lady, for example.
But then his teacher said something and the whole class was laughing their assess off. Bakugou in lead of course, moved to stand right next to Midoriya and when he thought it was ready, snitched the notebook out of Izuku's grip and blew it up.
"I still have things to settle with you, Good for nothing."
Scorched pages and black cover was easily not to rescue.
"I forgot there is a method that can be really effective if you want to become a hero so much," Kacchan said, turning his back on Midoriya and giving him one last stare. "Making the leap of the faith from the roof...believing with all your might that you will have an 'individuality' in the other world!" The laughter following this sentence was heartbreaking, as Bakugou left the room with empty eyes of broken person gazing after him.
It... wouldn't it solve his problems?
And only silence answered him as his breathing stopped.

People who are neurotic respond worse to stressors and are more likely to interpret ordinary situations as threatening and minor frustrations as hopelessly difficult.

"I'm never going to pass it!" Izuku groaned, hitting his head against the new, wooden desk in his now occupied room in Heights Alliance. The school was recovering from USJ Incident, where villains decided to approach them and attack, so everyone was on a high alert. Midoriya himself suffered some injuries, but All Might told him he had to move here, inside the walls of campus, to be safe and sound. Toshinori gave him a clear message why it was essential to change his living place and who was he to deny his mentor?
It was getting lonely in there. The building was meant to be for Class 1-A, but only he was rearranged (his financial problem was one of the reasons) and the rest of his big class will show up only after this semester ends.
And exam was coming, too. He spent nights and days on studying, but got distracted every time he opened a book.
But it wasn't like he wouldn't make it. He was smart [that invitation from Zurugashikoi was something after all] and needed a little time to understand. Yet his time was too short in his opinion, as his brain was taking its time. Much, much appreciated time.
A sudden and really loud bang coming from his door got him out of the train of dark thoughts he was swimming in every day. His head snapped and arms went up, curling, eyes closing, when someone approached him. He felt scared-and why the fuck he was scared, he had to be cool and collected, like a hero! WHY?
"Young Izuku!" a youthful deep voice shouted and Midoriya found himself face to face with All Might in his hero form and standard uniform. As always was he dripping with youthful power and cheerfulness, so realizing there was no danger, Izuku relaxed and dropped his protective stance (if you can call it a stance).
"All Might?" he said unsure, looking right into his idol's black holes of eyes. His smile slightly dropping and face scrunching up in worry and suspiciousness, All Might sat down on his pupil's bed and patted him on a shoulder.
"How are you feeling, my boy?" Izuku shuffled his feet, played with his navy blue t-shirt a little and tensed when felt the touch, eyes going wide and heart hammering in his tight ribcage.
Oh no, not another attack! he thought to himself, while covering his mouth with his open palm and flinching back from the big hand of All Might. His mind screamed DANGER DANGER DANGER and rang loud alarms, causing his thoughts to mix up and change. Where the hell disappeared his senses? What's wrong with him if the most vital and the simplest action was too hard and difficult for him? WHY WAS HE SUCH A DISAPPOINTMENT?
His breathing was slowing down and the Pro Hero noticed it, trying to calm his favourite student down.
"Izuku, listen to me, hear my voice, please," he said calmly, but Midoriya's breath caught up altogether. He was choking on his own, mind going blank, but Toshinori's hand keeping him steady in his seat. "Please, Izuku, just breathe."
And, fighting with himself, Izuku took a gulp of air.

They are often self-conscious and shy, and they may have trouble controlling urges and delaying gratification.

"U-U-Uraraka-san!!" he was running after her, going with such speed that he was surprising himself. Ochako smiled widely and dived right into the classroom, where Aizawa-sensei already dressed in his yellow, stylish sleeping bag was... well, sleeping. Or the boy thought he was sleeping, it kind of was looking like he was guarding and having an eye on all of the unruly teenagers. Said fifteen-year-olds were doing literally everything they could. Brushing and combing hair? Yes, of course. Floating in the mid-air? Yah, no problem. Playing hazardous games like poker? Kirishima wouldn't say no to cards. Trying to get everyone's attention?
...Well, that wasn't on Midoriya's To-Do-List, but it happened anyway. Ochako used her quirk to get out of the centre; Izuku couldn't get in the air, so when he crashed into the class and almost broke the door, every pair of eyes landed on his body, excluding the ones of Aizawa-sensei. Obviously.
Overwhelmed with this kind of focus on him, a low-pitched but loud sound escaped his lips. It'd been something akin to "EEEP!", but it would never sound the same in the boy's mouth. His cheeks flushed red, eyes going wide and grip on his books tightening.
"What the fuck, Deku? Just get to that goddamned seat, you shit!" Was the shout of Kacchan as he looked up from his closed position with a stare so hateful that was burning holes through his soul, Izuku conceded. It was weird. He quickly got to his seat and covered his face with a cover of his notepad with his hero's analyses. Midoriya was too awkward for his own good. And far too timid when among the crowds and more than three people.
"Do you need something, Midoriya?" asked his homeroom teacher as Izuku jumped in his seat, scared and frightened.
"N-no, sir," he mumbled, picking on his uniform again. Nothing at all.

People with high neuroticism indexes are at risk for the development and onset of common mental disorders, such as mood disorders, anxiety disorders, and substance use disorder, symptoms of which had traditionally been called neuroses.