My Hero Academia's turn! Beware, there may be SPOILERS for MHA if you are not up-to-date with the manga! SLASH, Harry/Aizawa.
I have three different ideas outlined for MHA - Harry with different attitudes/background/abilities/love interest in each one, but I'll only be sharing this one for now. I may come back to add the other two at a later time, or not, we'll see. I may also come back and explain my explanation for how/why this is legit Harry Potter crossover and not just a MHA with an OMC.
For now, lets just say Harry Potter and MHA timelines exist together in this universe and basically I'm saying the super powers are the result of the magical war in Britain (between Harry and Voldemort - Harry will be one of the first to develop this new "power" over in Britain).
Harry will have a soothing support quirk that refreshes anyone he touches, all of their stress, physical, mental and emotional baggage will melt away and only freshness and clarity will remain. It will feel like they were doused in bright sunlight, they will feel light and clean and like they are a brand new person. He calls it a Cheering Quirk (cuz it's awfully similar to a cheering charm/potion). He is asked to come to UA by Recovery Girl after the Hero Killer confrontation when Izuku is told he might never be able to use his arms again and All Might is exposed to the world. She feels his quirk can exponentially help the people at UA, especially since they'll all be living in the same place now.
He is an unknown support hero who lives in England, but he is part of a mostly secret Healing Quirk society, they keep in contact with each other because there are so few of them, watching each other's back and knowing who is best to call on when they need a specific kind of healing.
Recovery Girl tells the Principal, Aizawa, Toshinori, and the students of class 1-A that she has called in another healing Hero from England, his name is Solatium the Refreshing Hero. She explains his quirk and tells them he will be living with them as their very own healer. Uncomprehending they ask how he's a healer and she just smirks and tells them to wait and see.
When Harry arrives, he is greeted by Recovery Girl at the airport and they are driven to UA. When they arrive, school is in session and she is giving him a rundown of all the kids and the two adults he'll be watching over.
This Harry will still be 24 years old and a calm and confident person despite his rough upbringing. He is still short, only being 5'6'', so Aizawa and Toshinori are way taller than him, even some of the students are taller than him. His bright green eyes are behind simple but fashionable thin framed classes. His hair is shorter (think Ken from Digimon but it's ridiculously cute cuz it's curly as fuck).
The drawback of his quirk is that it takes some of his energy (just a small amount) which results in him always being a bit chilled, so he often dresses like he's in a cooler environment than he might actually be. When he arrives he's got on a soft as crap pastel green sweater with a scooped neck, showing off his collar bones and slender neck. He has on light wash skinny jeans and simple black tennis shoes with white ankle socks. He doesn't wear any jewelry or any other accessories, but he does have a light coat with a matching set of hat and scarf in his laptop bag just in case he has to use his power and gets colder.
He is introduced to everyone after class when they all come back to the dorm for dinner. He is cooking them something that smells great, Recovery Girl having already told them all that dinner would be served in the dorm that day to celebrate Harry's arrival. When they all come in, they are greeted by Recovery Girl and a beautiful foreigner. He introduces himself as the Refreshing Hero, Solatium, but says they can just call him Harry when they're in the dorm. Outside of the dorm he would appreciate them calling him by his Hero name, or Sol for short. They are all introduced and then Recovery Girl requests that Harry use his quirk on Toshinori, then Izuku, then Iida.
Intrigued, they are all around the table in the huge kitchen as Harry moved over to Toshinori and asks if he would like to be refreshed. He says yes and Harry asks for a high five. When their touch, Toshinori visibly deflates, Harry easily catching him and helping him relax into the chair. His entire being is transformed. He looks healthier all around, he doesn't sound like he's breathing badly anymore, he's relaxed and he mumbles something that sounded like "feels amazing."
Harry turns to Izuku who is staring at Toshinori with wide and surprised eyes that are full of unshed tears. Harry stops in front of Izuku and smiles gently and asks, "Would you like to be refreshed?" Izuku nods and hold out his uninjured hand, Harry takes it but pulls Izuku into a hug as he visibly relaxes as well. Izuku, was even more strung up (emotionally at least) than Toshinori, so while Toshi was half conscious, Izuku full on passed out in bliss. Harry gently moves him over to the couch and turns to Iida who, like the rest, are all watching him with amazement and some wariness as well.
Recovery Girl pipes up, "You're up next Iida, let him heal you and then we can all relax and enjoy this dinner." Harry shakes Iida's hand and Iida begins to cry, his friends comforting him as Harry goes to his bag and pulls out his hat and scarf. "What are those for?" Mineta asks, "When I use my quirk, it uses the smallest bit of my own energy. I basically amplify my energy to refresh those I touch, so the result is that I run colder than your average human and each time I use my quirk I get a little colder for a while." Harry goes and wakes up Izuku and all three of those he touched are now completely awake and energized, smiling and open for the first time in a long while. Dinner is a happy affair after that.
From there it'll follow the story, with Harry hanging around the school, he's eventually asked to teach when one teacher suddenly quits and they need a replacement for one of the Support classes. He spends a lot of time outside of teaching bouncing between Recovery Girl, Aizawa, and Toshinori depending on who's not busy at the time. In the evenings, he helps the kids with their homework if asked, refreshes Toshinori, telling him that little by little they can probably heal his wound so that he will not be so sickly, but whether or not he can return to being All Might is still uncertain. Strangely, after the first time Harry uses his refresh on Aizawa, he starts behaving differently towards him.
Aizawa will seek him out and initiate contact, having found out that Harry's quirk only activates when he directly asks someone if they want to be refreshed. He would put an arm around Harry's shoulder, fix Harry's hat/scarf if he's wearing it, touching their hands or thighs together when they are sitting, leaning his weight slightly on Harry if they're close enough. When in the dorm, Aizawa will go out of his way to be near Harry, sitting unnecessarily close on the couch or going to Harry's room whenever or inviting Harry to his room. Toshinori makes a joke that Aizawa is acting like a possessive cat and gets punched but Harry is embarrassed and yeah basically Aizawa fell in love with Harry's refreshing power, so he spent more time around him, then fell in love with him as a person (finding him ridiculously adorable and the perfect size for cuddling).
The Heroes in this fandom are fairly high strung and I wanted Harry to help them out a bit.