黒ギャル子ちゃんとしっぽり温泉旅行 ～Hしまくり三泊四日の旅～

The story revolves around Mukai Taichi, a second-year student at Aoi Academy, who is introverted and doesn't have a good relationship with his classmates. However, a girl named KazamiYukiho, known as Kii-chan, unexpectedly invites him to a hot springs trip as a penalty for losing a game with her friends. Taiichi is shocked by the sudden invitation, and despite his reservations, he cannot back out of the trip. The hot spring adventure between the introverted Taichi and the outgoing Kii-chan is about to unfold!

[Translated from the official site]