Triangle Heart(とらいあんぐるハートToraianguru Hāto), abbreviated as Toraha, is a series of H games and OVAs that is most noted for its spinoff series, Magical Girl Lyrical Nanoha. The name comes from the fact that each cast focuses on a "triangle" of one boy and two girls, though there are many other heroines. The Triangle Heart ～sweet songs forever～ OVA, based on the game Triangle Heart 3, focuses on a boy named Kyōya Takamachi who, with his cousin-turned-sister, vows to protect a childhood friend from a mysterious terrorist organization.