School Days ONA
The story centers on a love triangle between Makoto (the male protagonist) and Sekai (the heroines Kotonoha, Sekai). Makoto falls in love with Kotonoha (a girl from the same year, but a different class). He is not aware that they are both on the same train. Sekai, his classmate, manages to bring them together, despite strong feelings for Makoto.