A Misunderstood Deku

Beginnings

The Quirk Doctor:

"He has a vampiric quirk. His digestive system will slowly transition to a blood heavy diet within the next couple of years. After that, it will become blood only... I'm not even sure if animal blood will suffice." The man was blunt and straightforward with his diagnosis. This was standard for him at this point. Determining, through DNA testing, what quirk a child would be likely to unlock. At this point, he could tell that this kid would have a hard life ahead of him.

Inko Midoriya, the mother in this case, was stunned. Rightly so, considering how rare blood quirks were, and how her family didn't have a record of any in the past. "How?"

Looking over the medical files, he gave as best an explanation as he could. As much as he wanted to claim that he had all the answers, quirk science was messy. There were a lot of variables and it wasn't perfect. "It's recessive genetics on your husband's side of the family, it seems. There are records of another vampire quirk holder in your family."
Inko accepted the explanation. Instead of revulsion, however, she was determined to take every possible step to support her son. "Oh... what do I have to look out for?"

He gave his best estimate. Despite his experience, he'd never worked directly with this kind of quirk before, and so had to rely on witness accounts from other doctors. "Bloodlust is the real danger. The rest of the abilities can be trained properly, but that needs to be put under control fast. If not... well... it can put a lot of people at risk..."
"I see... I'll do that immediately." I would be a terrible mother if I didn't do what's best for him. "Is there a way to test which he would prefer?"

He nodded, "You can get animal's blood from the butchers, under the "Unique foods" sections they legally must have, but I'll fill out a prescription for human blood. Make sure you keep this with you at all times."
She accepted the note, determined to look after Izuku properly. "I will. Thank you, doctor."
He smiled, glad to see the best kind of parent. He heard from a different doctor of a couple who refused to entertain their daughter's blood quirk... and they both knew that story won't end well. "No problem!"

Izuku, meanwhile, was estatic at what he thought was a cool power to have, even if he didn't realize the downsides yet. If he was more jaded, he'd consider it a curse. "I can't believe I have a cool quirk!"

Inko smiled, glad to see her son happy, despite what she knew his future might be like. "It's a strong quirk, but you'll have to train it. You remember what he said, right?"

Punching upward in the air, he made his promise, "Yes! I'll do it!"

"Good! We'll do it together!"

Home at last:

When they got home, she immediately looked up different ways to help mitigate bloodlust in blood quirks. There was a lot of quacks, people claiming that starvation was a "cure", but that wasn't true. A site run by a trusted quirk doctor reccomended gradual exposure. The process was simple in theory... what wasn't was Izuku's quirk. It gave him essentially super strength, agility, reflexes, and senses... meaning that it would be much harder to do the exposure therapy safely. Using high quality rope, Inko tied Izuku to a chair. "Listen, the doctor says your quirk's downside is that you will berserk when you are exposed to blood... So to train that, I am going to expose you to blood now... is that ok?"
He nodded, completely trusting his mother's actions. While the boy was fascinated by quirks, he knew that if he didn't get a handle on his own, he'd never be a hero.

His mother reminded him, "You will have to resist any urges to get to it. Think of anything, just try your best... ok?"

He answered clearly, and she was able to clearly see his canines, far sharper and longer than her own. "I will!"