The story is about a love triangle between the male protagonist Makoto, and the two heroines Kotonoha and Sekai. Makoto develops a love interest in Kotonoha, a girl in the same year but different class. Although they both take the same train to school, she is unaware of his existence. His classmate, Sekai, manages to put the two together despite holding strong feelings towards Makoto.

[Source: Anime News Network]

A shy and insecure teenager, Itou Makoto, has resigned to stealing glances at a cute girl as they ride the same train each morning on their way to their high school. At least until Saionji Sekai surprises Makoto and chances a peek at a photo-snap of the beautiful Katsura Kotonoha on his cell-phone. After evilly teasing Makoto about his hopeless crush, Sekai offers to support him in his romance. So after many Makoto-pep-talks and lots of scheming, the three become close friends. Close enough that Makoto braves asking Katsura out on a date. And she agrees. Later that day, Makoto finds a quiet moment to express his thanks for all support that Sekai has offered him, and makes clear his intent on finding a way to repay her kindness. But he is totally unprepared and very surprised at the reward that Sekai has chosen. Sekai steals a long kiss from his lips, before breaking away to run for the train. Sekai turns and wishes Makoto well on his date...

[Source: anime.mikomi.org]

OVA that came with the PlayStation 2 game "School Days L×H"

Makoto, Sekai, Kotonoha, and many other classmates all go to a hot springs hotel to relax, where they discuss what their plans are for the upcoming Valentine's Day. When the day actually comes, half a dozen girls fight over who gets to give chocolate to Makoto.

[Source: Anime News Network]

Originally an April's Fool in 2007, this one episode OVA is a spin-off of the School Days game by 0verflow, and shows Kokoro Katsura, the little sister of one of the main characters, from her other side. A mahou shoujo out to save the world, or something like that.

[Source: AniDB]