BNHA verse: Streber can heal with his quirk, buuuut on other people only small injuries, if it's someone with a different blood type. With himself and people with his same blood type, while he can't heal anything deeper then a small stab wound he can heal with the only downside being a small headache, nose bleed, and light headedness. He can heal more serious injuries on other people but and this also goes for people with his same blood type. His blood oxidizes at a very fast rate, a "nefarious black ooze" comes out of his mouth, eyes, and nose, and he passes out completely. However long he's passed depends on how serious the injury was on the other person, and how much he pushed his quirk before healing. Sometimes it can be up to only few weeks or just a few days and sometimes it can be a few months. Even with blood transfusions it just takes time for his white blood cells count to catch up again and his body to fully heal. Streber doesn't use the healing aspect of his quirk unless it's under very very extreme circumstances.
After the liberation war it took him about 4 months to wake up, due to a very bad combination of obviously over using his quirk and using his healing trick on a student who was in pretty rough shape. 😔