Harem

Harem - This extraordinary quirk permanently links the user (the "master") with anyone they bring to orgasm, pulling their quirk into the user's own pool of abilities. The harem members can no longer access their own quirks by default, but instead, the user can distribute powers at will to their Harem, though only one quirk may be active per member at any given time (with the exception of the user, who may always have this active, and up to one other). This quirk also optimizes the user to a form well suited for maximizing it's abilities on the most targets possible.

Caveats and Clarifications:
-The user becomes a very well endowed futanari, with enhanced sexual traits and a very enticing appearance and scent.
-There is no limit to the number of people who can be given the same quirk, so long as they are given only one.
-The master may choose to willingly revoke their connection and lose all associated effects from the member and themselves.
-The user must directly bring the target to orgasm while using their own body. Hand, penis, mouth, etc all count, as does orgasm while the target is masturbating and being stimulated at the same time, but being the subject of a fantasy or other indirect, nonphysical stimulation does not count.
-There can be special interactions between quirks when the same person has two quirks, as well as when two people share the same quirk. For example, when two people in the same harem have Harem Master, both can recruit people, but the original owner has ultimate authority over the ability.
-As the harem grows, the ability grows stronger, so limits may change or reduce as certain thresholds are reached.

This is the quirk that Izuku Midoriya wakes up with, though he doesn't yet know it, or the new...condition "he" is in.
Instead, he feels the worst he's ever felt in his life. Sick, starving, dehydrated, and sore...but alive, and being awakened by someone's voice, asking him if he can hear them.