Amane Switch ~Yamanai Ame to Yanda Kanojo Soshite Ore~

Shinji Mizushima leads a normal life with average athletic and academic performance before becoming acquainted with a mysterious girl named Amane Satonaka.

Shortly after Amane transfers to Shuei Academy, Shinji finds himself drawn to her when he sees her standing outside in the rain without an umbrella, humming a melancholic melody to herself. The sight of her figure drenched in the downpour of rain is so beautiful it seems otherworldly to him. In that moment, her existence becomes transcendent.
Transfixed, Shinji can only watch in amazement until he realizes the beautiful girl before him is on the verge of collapsing. He rushes to her, catching her in his arms. He does not yet realize that this moment will change his life forever...

[From Steam]