Triangle Heart

is a Japanese series of eroge and OVAs that is most noted for its spin-off series, Magical Girl Lyrical Nanoha. Its core trilogy games were published respectively on December 18, 1998, July 30, 1999 and on December 8, 2000. The OVA adaptation entitled Triangle Heart: Sweet Songs Forever (とらいあんぐるハート～Sweet Songs Forever～) which is based on the third game, was released by Discovery Studios on August 28, 2000.

Triangle Heart 1
Years ago, professional bodyguard Shirō Fuwa and his client Albert Crystela were killed by a terrorist organization that is known by the symbol of a clover leaf. Albert's daughter Fiasse blamed herself, but then grew closer to the Fuwa (now Takamachi) children, Kyōya and Miyuki, and decided to use her gift of singing to help the world. But now that they have grown up, Fiasse herself is being targeted by the same organization. Kyōya and Miyuki, swearing to protect Fiasse, become professional bodyguards like their fathers.

Triangle Heart 2: Sazanami Joshi Ryo
Kyosuke Makihara works as a substitute janitor of a huge boarding house called Sazanami Dormitory mostly consisting of young school girls from elementary through high school, while the regular janitor and the dorms owner, who is his brother-in-law and his aunt respectively, are travelling abroad in Hong Kong. The story follows the lives of Kousuke and the girls and introduces each them one by one.

Triangle Heart 3: Sweet Songs Forever
A mysterious organization keeps sending intimidating letters to Fiasse Christella, the principal of British Christella Music Academy. The purpose is to find the whereabouts of Fiasse's inheritance; although Fiasse already has a bodyguard, Ellis McGaren, she asked her childhood friends, the siblings Takamachi Kyouya and Miyuki to help Ellis. This of course is received by Ellis, as a professional bodyguard, with a cold shoulder. Kyouya remembered an incident that was happened several years ago, when he was about ten years old. This incident was actually aimed at Fiasse's father, senator Albert Christella.