Hayakita Otoha

Otoha accidentally joins the summer camp her brother Itsuki is on when she boards the wrong bus by accident. Because she's already familiar with Itsuki Rio encourages her to have sex with her brother in front of an audience to ease her into life on the island.

Although she knows she's not supposed to according to the rules on the island she is jealous of her brother having sex with other girls. Also she's willing to have sex with any other girl who asks but won't let any boy have sex with her but Itsuki.

Because they're siblings they are given a room together. Otoha uses the opportunity to wake her brother up each day with sex.