悠木勇

就读于东京的大学的一年级学生。现在与姐姐伦同居中。姐弟关系非常好，经常被误认为是情侣。但只把她当成关系好的姐姐，是极其健全的姐弟关系。过去没有交过女朋友，至今仍是处男。

摘自本作简介中该角色的段落

Isamu is the younger brother of Rin. Now an university student, he lives with his older sister in the same apartment to save some money. Isamu is really happy to live with his sister because she is very kind to him. Loving her a lot, he sometimes wonders if he have a sister complex. Some time after settling down, he worries that his sister is coming back late at night and she confesses to him that she is an AV actress. He is not very keen to learn about his sister's activities but out of curiosity, he secretly decides to go see what kind of videos his sister turns. He then sees the first video of his sister where the actor asks her some questions about who she is and about her past experiences. She answers and he then sees his sister taken in doggy style and in various positions, groaning of pleasure. To his surprise, he finds his sister super exciting and starts to jerking off on her video. Now a slave to this permanent desire, Isamu begins to have mixed feelings : the feeling of desire to see even more videos of his sister, the feeling of taking her for him alone and the feeling of protecting her ...

简介来自 VNDB

東京の大学に通う1年生。 現在、義姉の倫と同居している。 姉弟仲は非常に良く、カップルと間違われることも多い。 しかしあくまで仲の良い姉としか見ておらず、至って健全な姉弟仲。 過去に彼女がいたことはなく、いまだ童貞。

简介来自 Bangumi