MHA: the Paleomorph Hitman

in a world of Quirks, a sexless child who is a chirmera in appearance, and a daughter with green hair is born to Inko and Toshinori Yagi.

the girl is named Izumi, and the chirmera is named Izuku.

that's the start of Izuku's hell, he quickly matures into an adult by age 4, and learns he can become any prehistoric animal species to ever exist. and this only increases his torment. he becomes invisible when he's quiet, and tormented by Inko when he talks.

leaving home, he becomes a hitman where his targets disappear. the only sign being a blood soaked location.