Ichijou Shizuka

A doctor who drifted ashore with the main characters.
She is intelligent and calm, with a constant smile on his face.
She is the first to notice the existence of the virus that has attacked the heroines and recommends that the heroes rape them as a vaccine to temporarily suppress the virus, and she herself engages in intercourse with the heroe while developing a cure in the abandoned facilities.

In the process of developing the cure, she teaches the hero various techniques in order to collect his semen on a regular basis.
She is the only ally on the island who has no dislike for the protagonist.