Takou no Koori-hime wo Tasuketara, Otomodachi kara Hajimeru Koto ni Narimashita

Souta Minori, an ordinary high school boy, rides the train with a beautiful girl from another school, Nagi Shinonome, nicknamed the "Ice Princess” for her cold and off-putting attitude One day, Souta notices her being molested on the train, and he summons up his courage to intervene and rescue her....

Source: MyAnimeList