(I have three different versions of his information. The first is the most complete, though only the last one has his reason for being a hero.)

Forms

Yamiyo (闇夜) Llew (Yamiyo: First name. Means "dark night." Llew: Family name. Welsh. Means "lion")

Quirk: Ever since quirks appeared, there has been a Welsh family with a single mutation-type quirk that has been passed down through all the males and, very rarely, a daughter or two, that is, very simply, referred to as "neko." It manifests at birth, as opposed to around ages 2-4, and grants the person distinct feline characteristics and behaviors, the extent of which vary, but always include catlike senses (which includes night vision at the cost of being colorblind), ears, tail, claws (though Yamiyo's are retractable and slide over his regular fingernails), and sharp teeth. In addition to these, Yamiyo has a tendency to purr when happy and meow when startled, a slightly rough barbed tongue, vibrant emerald eyes with feline pupils, the ability to transform into a regular house cat (though this transformation is painful and draining, so he only does it if absolutely necessary), the ability to recharge with quick naps anytime, and anywhere, he pleases (this is a necessity, as his duo of quirks requires him to sleep a MINIMUM of thirteen hours a day or he gets cranky and can't control his second quirk, though he's been getting a lot better, as he used to have to sleep eighteen hours), incredible agility, and he lands on his feet most of the time. A few drawbacks of this quirk, besides what's already been mentioned, are his sensitivity to loud noises, bright lights, and bad smells, and his very feline playfulness; a laser pointer or wiggling string very easily captures his attention.

His second quirk is from his mother and is called Soul Shadow, and it creates an impenetrable darkness in the perception of anyone within range and causes voices to whisper their shortcomings or otherwise use the cracks in their psyche to cause them to break down. It doesn't actually create any shadow or sound, since it's purely in the victim's head. The biggest drawback is that, if it's not controlled or if it's used to much, the user becomes afflicted and forgets to turn it off unless they pass out or something manages to break through their self-induced trance. Yamiyo has been training this quirk the most, and has been getting much better at controlling who is affected by it, though it's very hard for him to practice, as he hates hurting or scaring people, and the incident with it that caused his family to move from Wales all the way to Japan still haunts him, making him withdrawn and aloof.

Family: His father is Oliver Llew, and he has the most basic version of the Neko quirk, and his mother is Sakura (桜) Llew whom he inherited the Soul Shadow quirk from, and whom he looks up to the most, since, despite her quirk being deemed "villainous," she didn't let it get to her and she met Oliver through an exchange program at her police academy. He also has an older sister named Aderyn who inherited her quirk, Telepathy, from Sakura's father and uses it in her occupation as a lawyer, and younger twins, the brother, Eurion, with the neko quirk, and sister, Chuya (昼夜), whose quirk hasn't yet manifested.

Appearance:Yamiyo is short for a boy, at only 5'1", half an inch shorter than Uraraka Ochaco, not including his ears, which would add another three inches to his height when fully perked up. He has pale skin, bright green eyes, and jet black hair and fur. His tail is three and a half feet long, as it's needed for counterbalance, and his fur is fluffy and soft.

Sexuality: Very gay.

Yamiyo Llew is a "Hafu" or someone with one Japanese parent and one foreign parent, though he grew up in his father's home country of Wales and only moved to japan with his parents and three siblings in the past year. Despite this, he is fluent in Japanese and has no issues conversing with or understanding others, though he's generally withdrawn and aloof, which is partially due to his homosexuality, though mostly to his most dangerous quirk. He has two very distinct quirks, the first and most obvious of which is a mutation-type quirk simply called Neko. The most obvious features of this are his ears and three and a half foot long tail, though he has other qualities as well, which will be detailed as the story progresses. His second quirk is one that he hates, and isn't very good at controlling, called Soul Shadow, which confines everyone in its area of effect, or AOE, into the darkest recesses of their own minds and cuts off their senses as they're tormented by whispers saying everything that hurts the most. Despite his "villainous" quirk, he's determined to be an amazing hero one day, and worked hard to get into UA. He's small, even shorter than Uraraka Ochaco if his ears aren't counted, and quite cute with his delicate features and large emerald green eyes. That being said, he isn't someone to be messed with, let alone woken up from a nap.

Name: Llew Yamiyo (goes by his given name, Yamiyo, as opposed to his family name)
Hero name: NietClat (welsh for night cat)
Age: 15
Gender: Male
Sexuality: Homosexual
Looks: Yamiyo is short for a boy, at only 5'1", half an inch shorter than Uraraka Ochaco, not including his ears, which would add another three inches to his height when fully perked up. He has very pale skin, bright, round green eyes with catlike pupils that narrow to slits, and jet black hair and fur. His hair is short and kinda jaggedly cut, and tends to stick up if he doesn't comb it or it gets ruffled. His tail is three and a half feet long, as it's needed for counterbalance, and his fur is fluffy and soft. He's slender and slightly toned, but not overly muscular, and his ears have extra tufts of fur at the tips similar to a lynx's. His tongue is slightly rough like a cat's.
Personality: He's very sweet and kind, but he is also very shy and timid, which has to do with being bullied his whole life for his secondary Quirk. That being said, he's doing a lot better at handling bullies, especially if they're bullying other people, and, once he stands up to someone, his confidence is boosted dramatically and will continue to do so. He loves to cuddle, but is far too shy to initiate it. Has a tendency to purr when happy and growl when angry or frightened, and is also easily distracted by laser pointers or loose strings.
Quirks: Neko and Soul Shadow. Neko is pretty straightforward, as he has physical characteristics of a housecat, including a direct translation of their strength and jumping abilities. He has retractable claws on his hands and feet that slide over his finger and toe nails as well as sharp teeth. His tail acts as counterbalance, allowing him to land his on his feet and change direction midair as well as make sharp turns when running. His senses are extremely strong and he has night vision at the cost of color vision, so everything is in greyscale. Soul Shadow is a bit more complicated, as it effects people's brains directly and targets the trauma and self doubt someone has and amplifies it until the victim can't register anything else except their own negativity in their head, which can utterly destroy their psyche if exposed to Soul Shadow's effects for too long.
Quirk weaknesses: Yamiyo has to sleep for fifteen hours a day to function properly when awake and help prevent accidental activation of Soul Shadow, he is extremely sensitive to loud noises, bright lights, and foul smells, as well as being easily distracted by small moving objects. Soul Shadow is very difficult to control, and isn't precise. His current smallest radius is 20ft in every direction, affecting everyone in that area, regardless of physical objects in the way and without differentiation of friend or foe. If used for too long, accidentally activated in response to a strong negative emotion, or if he tries to restrain its effects to a smaller area or just specific people, it effects Yamiyo, as well, and he can no longer stop using it unless he passes out or his body receives a significant amount of damage.
Crush: Bakugo
Rival: Doesn't really have one, though he tends to argue with Bakugo a lot.
Backstory: The Neko Quirk is passed down through the men in his dad's family, and he gets Soul Shadow from his mom. His dad is Welsh, and his parents met through an exchange program between their police force colleges, and his mom, Sakura, moved to Wales to marry his dad, Oliver, soon after they graduated. Yamiyo grew up there with his parents and older sister, and, while his family loves him very much, Soul Shadow caused him to be bullied and feared ever since it manifested. One of his biggest fears is accidentally activating it around his family, particularly around his baby brother and sister. The reason his family moved to Japan is because, not long before he graduated middle school, the bullying came to a head and Yamiyo accidentally activated Soul Shadow, affecting his entire school until he passed out from exhaustion. His parents struggled to convince their colleagues that the young teenager wasn't a threat to society, and decided to move to Japan where Yamiyo's grandfather could help him learn to control Soul Shadow like he helped Sakura. There, he applied to several hero schools, including UA, and just barely managed to pass the physical portion of the entrance exam, getting by on mostly rescue points.
Reason for being a hero: He loves helping people and he also wants to prove everyone who called his Quirk "villainous" wrong. He doesn't care if he gets famous or rich as long as he can save people who need help and prove to kids with Quirks that aren't conventionally "heroic" that they can save people, too.
Other: Rubbing his ears or the base of his tail turns him on. He's definitely a bottom/uke. He enjoys people watching and is very perceptive of people's emotions.