So just to point out some information before we begin. I'm putting some of the more important changes in for these characters. Also to add a little more spice, Izuku and his sisters in this will have pact statuses. If you don't know what this implies, look up omegaverse.
Izuku Midoriya: age 14
Race: Nekomata
Pack status: Alpha
Izuku was the older twin of him and Shirone(Koneko) and ran to the human world out of fear when Kuroka killed her demon master. With nowhere to go to, he found his way to Inko Midoriya's doorstep who he knew from the past. He dies his fur with a tint of green as his way to hide in the human world and uses very little of his nekomata powers to avoid drawing attention. When he does however, he's very mindful to not lose control of himself and become what Kuroka had. For an alpha, Izuku is pretty docile, but is not afraid to drop it if you anger him or wish to insult or harm someone he likes as a friend or future mate.
Likes: Tuna, Sweets, Soft things, Katsumi and Ochako, Warm days, All Might, Heroes, Mitsuki and Inko, and Shirone
Dislikes: Rain, Baths, Perverts(He can smell them in this), Villains, Devils, and Kuroka
Inko Midoriya: age 40(She'll look the way she does in Canon at this age)
Race: Human
Pack status: NA
Inko had made a devil contract with Kuroka a few times in the past to know Shirone and Izuku personally. Once she found out about what happened, she immediately brought Izuku into her home as shelter knowing that devils would be after him. She cares for him like her own and wishes for him to forgive himself for what happened in the past knowing he panicked and acted on survival instinct. Inko is basically the same in nature as in the series with no real changes after this.
Likes: Izuku, Shirone, Spending time with Mitsuki, Katsumi and Ochako, and pleasant outings
Dislikes: Violence, Villains, Devils, Kuroka, and aggression
Katsumi Bakugo: age 14
Race: Human
Pack status: NA
Katsumi has been friends with Izuku since they were 5 and has a large amount of love and respect for him. She'll also carry tuna with her for Izuku when he's down and depressed to perk him up. During their first year of middle school, Katsumi learned about Izuku's origins from Inko and roughly understands his situation without knowing about devils and angels. By the time the story takes place, Katsumi and Izuku would have already done it with her trying to calm his heat cycle after finding out the truth(He's still a cat, so he will have feline tendencies). She is also good friends with Ochako and wants her to convey her feelings to Izuku.
Likes: Spicy food, Mountain climbing, winning, Ochako and Izuku, Explosions, Inko, Heroes, and Shirone(from what she's heard of her)
Dislikes: Losing, Weaklings, Authority, Perverts, Kuroka, and Villains
Ochako Uraraka: age 15
Race: Human
Pact status: NA
Ochako had came into Mustafar middle school around her second year and could barely make friends. In an effort to try and help her, Izuku had went up and talked to her with Katsumi following and not caring to start. Eventually, these two became the best girlfriends one could see with a mutual respect between the two. Ochako secretly likes Izuku, but is too scared to say something to him. In an effort to help her, Katsumi puts her in many positions to which she can get the courage to say how she feels for Izuku. She's pretty normal compared to how the actual series portrays her and has the same goals for herself.
Likes: Starry skies, Japanese food, Mochi, Izuku and Katsumi, Shirone, Inko and Mitsuki, Her family, and Heroes
Dislikes: Perverts, sour things, Rude people, and Kuroka
Kuroka: age 24(They never give an actual age in this)
Race: Nekomata
Pact status: Beta
Kuroka had done the same things she did in the past and is with the Chaos Brigade. She looks constantly for a way to take Izuku and Shirone back as her's, even by force. She does not care much for taking things serious, and will mostly play with her opponents until provoked enough. She will make her appearance in this series before Koneko as someone assisting the League of Villains.
Likes: Shirone and Izuku, Lazing around, Tormenting others, and Giving Pain
Dislikes: Hard work, Heroes, Authority, and Ochako and Katsumi
Koneko Toujou(Shirone): age 14
Race: Nekomata
Pact status: Beta
For the most part, Koneko is taken into the Gremory house like in the story with no difference. The only major thing is how much guilt she feels knowing she may have sent Izuku to his death without stopping him. She has absolutely no idea what happened to him and fears the worst thing imaginable could have happened to her older twin brother and can't forgive herself for it. Koneko will make an appearance later in the series, but will be talked about before her reveal.
Likes: Sweets, Comfy areas, Gremory house, Izuku, Ochako and Katsumi(when she meets them), and warm days
Dislikes: Perverts, Strangers, Kuroka, and People who don't try
Sona Sitri: age 18
Race: High class Devil
Pact status: NA
Sona will be the one that is attacked by the sludge villain in this with Izuku saving her. Ordinarily, she would be fine being attacked by a weakling. But thanks to Izuku's selfless heroism, this sparks an interest in her for him and makes them interact more. Sona will eventually make these feelings of interest into love and show more emotion around Izuku. She won't know of his lineage until later, but Izuku will know she's a devil by how she smells.
Likes: Books, Silence, Izuku, Rias, and Her devil house
Dislikes: Perverts, Insubordination, weakness, Arrogance, and Villains
This won't be a project I'll start till I finish The Great Izuku, but I will post the harem Izuku will have in a day or two. If anyone wants a certain Highschool DxD member in the harem, make a comment down below and I'll see about it.