Izuku Midoriya is not human. He is a very rare mutation, that people born qrirkless have a chance of getting. This is that they can be born a witch. Being a witch is not a quirk, and it mostly has to do with how they affect the inviorment around them rather than having a power in themselves.
Witches are born with instinctes, much like animals. They know how to cast spells, how to brew potions and what ingredients are needed for different ones. They also are aloud up to three familiars to help them with their jourenies.
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One day walking home to visit his mother after school, Izuku makes a detor through a forest to make sure all was well, when he stubled apon a little baby. upon further inspection, Izuku relizes that this baby was a witch as well, and recently born. With motherly instincents, Izuku brings the baby to his little treehouse in the forest and raises him as his own.
So I'm bad with description so I'll go with this. In this story izuku midoriya was born quirkless until the league of villains capture him and then turn izuku into a nomu, giving him multi quirks. Izuku then creates his own quirk, mixing all of his quirks together, creating OFM, which is stronger than OFA. If you wanna find out more read on!!