Semi and Semichan

A high school student named Semi Yuki, who lives alone in the countryside, hates summer and cicadas. However, when he returns home from school the day before Christmas Eve, an unknown girl has somehow entered his house. The girl introduces herself as Semi-chan and thanks Seki as her benefactor, but Seki has no recollection of this whatsoever. Seki attempts to call the police, but perhaps due to impure thoughts, he ends up letting her stay at his house for the night. On Christmas Eve, the two of them decide to visit the place where Semi-chan claims to have seen Seki... but... *Although a certain keyword is attached, it is set up so that anything works for the protagonist.