(Thanks to @CrystalShimura for the suggestion! Sorry if it isn't as good as you had hoped. Also I got the quirk idea from @closetpasta. Well sort of- ) 

 Quirk name: Fear Flame

Function: You can make a selected group of people (Maximum is 5) feel a sudden rush of overwhelming anxiety or fear, then manipulate fire to make that image in front of the selected few. User can do so for two minutes to everyone they use it on. 

Drawback: Users heart rate speeds up about 2x more for every 13 breaths they take, and they get slight heart burn.  

Y/n sits on her bed, scrolling through (Favorite social media app) when she suddenly gets called by Eraser Head. She picks up, sighing a bit. "Hello?" She asks, Eraser Head suddenly starts speaking. "H/n, you've been given a mission. By the government personally." he states with a gruff voice. She tenses up. She hasn't had a mission for over three months. She wanted to have one for so long, she couldn't wait to try her new technique out on a villain, but this time... this time was different. 

"There's a Villain they just recently found out about and everyone else is busy. They want you to find and secure him. If you're able to, possibly also fight him carefully. You may be one of the less used heroes, but you're dependable and honest. You work hard and keep a level head during stressful times." Y/n smiles at his words, thankful that her once middle school enemy, is now treating her with the respect she's always wanted. "You can count on me." She says eagerly. "I'm glad." He mutters than hangs up. "Alright.. they're counting on you Y/n! You've gotta make sure you don't screw this up!" Y/n quickly gets her hero costume on and runs to her apartment door. She puts her keys and phone in a secret pocket, turning her ringer off so that it won't distract her later. She opens the door and sees Katsuki outside. Her facial expression shifts a bit. "Hey katsu.. what are you doing here?" She asks walking over to the blonde. "To make sure you were actually gonna go. everyone knows that you're the laziest when it comes to getting out of your house, especially at night." He grins a bit. Y/n rolls her eyes and walks past him. "Yeah right." "Just come back safe.. We can't lose anymore heroes.." He says holding a crimson R and a red shoe. She swallows back her emotions. "I know.. I won't lose." He nods as she walks off. Katsuki looks down at the last pieces of his friends he'll ever see. "Izuku... Eijirou.." His eyes tear up. 

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Y/n climbs on top of a banister and looks around. 'it's so hard to see when it's so dark.. too bad the moon is only a crescent tonight.' She thinks looking around with only half the light she needs. The shadows blur her vision and make her skin crawl just thinking about what could pop out of there and snatch her toes. "Yeesh-" She twitches with goosebumps. She than looks around and notices a suspicious, dark figure walking around the empty streets. Not even the light posts were on. It's possible they could be broken... or maybe someone's quirk. Whatever it was, it was bringing an anxious feeling to Y/n, making her spine grow chills and her feet shuffle back a bit. Even though she doesn't have much fear herself, she does get quite nervous, knowing that she doesn't know what people are capable of, and shouldn't mess with the unknown. But it's her mission to do the exact opposite and she decides to investigate, despite her gut feeling telling her to retreat while you still can. So gathering up all her courage, she walks quietly after the dark figure. 

'I'm still in Musutafu.. but it seems like we're headed towards Tokyo in about 3 miles..' She says peering from a corner. The figure's eyes seem to glow when they turn their head slightly, It's a faint glow of ocean teal. They say the eyes are the window to the soul.. but this soul seems to be lost, locked somewhere with noway to get out. Constantly searching for a way to break free. Even just for a simple friend to understand. Y/n recognizes those eyes, they look like her father's. Even though there are others who have the same eye color, her family's eyes have a specific tint to them, and whenever she sees it, she can't help but feel her stomach clench up. It's as if she's connected to those eyes in particular. Now her quirk couldn't be used on herself, but she sure was afraid of who that might be.. her younger brother went missing when she was younger. By the feeling she has.. she thinks it's him. But the black bush that covers his head isn't the same as her brother's, his was red.. or at least she thought it was. 'It might just be the shadows...or it could be dyed-' She thinks, starting to forget about her mission as her mind wonders onto other topics. Soon enough she gets so caught up in her thoughts that she ends up bumping into the back of the figure. He slowly turns around, and glares into her soul. She snaps back into reality and steps back. 

"Hey shorty. Watch where you're going." He groans out, sounding less than happy. You're ear twitched at the word short. "First of all sir.." you put her finger in his face, "I am not short." he gives you a bit of a confused/bored expression. "Second of all... you can shut your patchy looking self up with your DIY hair and your old ass wrinkled cloths. You're over there looking like a whole emo Pomeranian, don't talk to me like that, unless you want a one way ticket to hell. The next thing that comes out your face better be smart, or i'll have no choice but to beat the shit out and some sense into you-" She places her hands on her hips. "BAHAHAHAHA" They both suddenly burst out laughing-

*BEEP*

A shiver goes down her spine, her fingers and legs tingle with a slight hint of fear. 'He's not that scary.. at least not like father..' She takes a step back, gulping a bit. The silence of the street made the tension between the two even worse. She clenches her fist, he raises his hand and before she could move, he blasts a vortex of blue flames at her. Her eyes widened and she felt a sudden rush of fear cower over her. She saw light flash before her, but when she blinked again, she was surrounded by darkness. She covered her face, tears running down her face. 'Am I dead?.. Is this what death feels like?..' She thinks wiping away her tears as her sobs could be heard by the male in front of her. Her eyes get adjusted and than she sees her legs and hands lit slightly by the light of the half moon. Her quickly realized she wasn't dead. She looked up at the raven haired male and was slightly confused, but also grateful that she wasn't dead. After all, she had promised Katsuki that she wouldn't die. 

The male in front of her stared at her trembling body, not feeling any emotion, well except for the slight guilt of making her cry. He hadn't seen her for a long time, and thinking of killing her made him sigh. She swallowed back her fear and spoke up, "How did you miss? I was right in front of you.." He tilts his head down and his hair covers his face. "I'd rather see you fight first before making the decision to kill you." He says blankly. "I-.." She was speechless. She hadn't known some villains actually are fair. She just always assumed they were heartless beings with personal problems that they couldn't solve and now they're out to solve them with crimes. Or something like that. "So get up and we can settle this. Like sane people." He says stepping back into a fighting stance. She gets up and wipes her cheek with her shoulder. "Alright..." He raises his hand again and sends another spiral of flames her way. She dodges this time and runs under them, he moves the flames as she does. Her eyes widen and she jumps to dodge the flames. He uses his other hand to block her exit, she jumps back, pupils contracting when the bright blue flames just barely hit her face. He chuckles a bit, stopping his flames to give his hands a quick break. She doesn't waste any time with the opportunity that she's given, she quickly runs up to him, grabs his face and stares deep into his eyes. Her pupils glow slightly and then she backs up about five yards. "Got it."

A shiver goes down his spine and he's suddenly paralyzed. 'What's going on?.. What did she do?-' His thoughts were interrupted but darkness surrounding him. H/n stands in front of him staring into his now pure white eyes, she sees into memories that gave him his fear then she puts her arms out in front of both of them and manipulates her fire. It coils down her arms and around her fingers, soon enough being soaked into his brain. His paralyzed eyes suddenly widen.

"No... father... please!" *cough* "I-" *cough* "Can't... continue..!" A young redhead sobs

"Silence! Continue your training!" The young boy's father smacks him.

"Ahh! Please...!" He cries even louder, his skin burning, slowly turning a purple color as blue flames make their marks.

Dabi's face is streaming in tears as he covers his neck and arms. "P-Please! Father...! Stop! I-I can't anymore!!" He cries crouching down. H/n's eyes start to water. 'I'm sorry...' she lets out a shaky breath, goes behind the male and cuffs his hands, putting a soaked towel over them. Her quirk wears off on him and his cheeks are left with tear stains, he breathes heavily, getting adjusted to the light. He looks back at the girl, trembling with fear, "Y-you.... M-monster..." he says breaking down.

She never knew her quirk could work like that...She was heartbroken, she didn't like villains, but this one felt.... Close.

She takes him to the station where Eraserhead meets her there. "I knew you could do it H/n." He says with a slight smile, "Well... it was a painful job.." She looked over and saw them put a muzzle on him. He was jumping at them and trying to attack them, like he had lost his mind. He didn't act anything like this before. She felt that it was her fault.....

"Hey! Stand down!" Eraserhead holds the male with his scarf, his hair stands up and his eyes glow red, he erases the males quirk just when he was just about to use it to bust out. Frightened and confused, she pushes Eraserhead, making him blink and fall over, she then pushes the cops away and stands protectively in front of Dabi. The male's eyes widen a bit, but he calms down. "H/n..! What are you doing?!" Eraser head asks standing back up. "I-....I-I.." She looks back at the male and they make eye contact. Her eyes widen a little as they fill with tears. She saw the sorrow, the despair... the hatred and pain in his eyes. Her heart clenched and something snapped inside of her. She turned towards Eraserhead and stands her ground with a serious expression.

"I'm protecting my brother."