Shiraga Airi♀

Tooru's cousin. A shy girl who always finds it difficult to express her feelings and often acts like a small girl. The two met about 10 years ago when they were very young, but reunited on this island after Airi transferred to the school that Tooru works in. Tooru’s mom, who knew about Tooru’s whereabouts, decided to “secretly” move all of Airi’s stuff over to where he lived, so Tooru can be a guardian for his cousin who he hasn’t met in 10 years.

[From Danny Choo's blog and Visual Novels and Eroge Review]