Hisashi Midoriya is not Izuku's biological father.

After a freak accident left him sterile, Hisashi and Inko approach one of his oldest friends: Enji Todoroki. Still mourning Touya, Enji is hesitant to get involved, and only does so after a deal is made with firm, but fair terms. 1. The child is to be made aware of their parentage if they ask. 2. If the child asks, Enji must meet with them at least once. 3. The child is to be loved and cared for, no matter what quirk they have or don't have.