"Triangle Heart: Sazanami Joshiryō" is a three-episode OVA series that serves as a spin-off to the "Triangle Heart" visual novel series. The story is set in the fictional Sazanami Girls' Academy, a prestigious all-girls school where students train in both academics and combat skills. The narrative centers around Nanase Takamachi, a skilled swordswoman and the student council president, who is tasked with maintaining order and protecting the school from external threats.

The plot begins with the arrival of a new transfer student, Akira Takamachi, who is Nanase's younger sister. Akira, though inexperienced, possesses a strong sense of justice and a desire to prove herself. Her arrival coincides with a series of mysterious attacks targeting the academy. These attacks are orchestrated by a shadowy organization seeking to exploit the school's advanced combat training programs for their own nefarious purposes.

Nanase, along with her close friends and fellow students, takes on the responsibility of investigating and thwarting these threats. The group includes Kyouya Takamachi, a skilled swordsman and Nanase's childhood friend, and Miyuki Takamachi, another sister who provides tactical support. Together, they uncover a conspiracy that threatens not only the academy but also the broader community.

The series balances action and character development, showcasing the students' combat abilities while delving into their personal struggles and relationships. Nanase's leadership and determination are tested as she navigates the challenges of protecting her school and family. Akira's growth from an inexperienced newcomer to a capable fighter is a key focus, highlighting themes of perseverance and self-discovery.

The OVA concludes with the students successfully defending the academy and uncovering the true motives behind the attacks. The resolution reinforces the bonds between the characters and sets the stage for potential future conflicts, leaving the narrative open-ended yet satisfying. The series is characterized by its blend of action, drama, and light-hearted moments, making it an engaging entry in the "Triangle Heart" universe.