Chinmai Kyuuketsuki no Ojou-sama ni Torawareta Ore wa Nyotaika Saserarete Juujun na Imouto Maid ni Choukyou Sareteshimau Sou Desu | ちんまい吸血姫のお嬢様に囚われた俺は、女体化させられて従順な妹メイドに調教されてしまうそうです。

Mitsuru Yokomizo, the protagonist, was stranded in a snowy mountain, but as he walked, he somehow found himself in a mysterious forest. There, he met Chris and Canon, vampire girls. Mitsuru had his blood sucked by Chris and turned into a girl.

The girlified Mitsuru was given the name "Maron" by Chris and forced to work as a maid in the mansion where she lived. Furthermore, Mitsuru is taught the pleasures of a girl's body by them. Each time he experiences pleasure, Mitsuru notices that a different ego is sprouting within his mind.

The girl's ego emerges to the surface of Mitsuru's consciousness and begins to move his body in his place──