At Ikaruga High School, sisters Kotono and Suzuyo arrive under the watchful eye of their mother Kasumi, who leads the board of trustees. Both girls quickly develop a quiet admiration for upperclassman Shoichi, yet his interests lie with the school doctor Maiko. Facing expulsion over failing grades, Shoichi accepts Maiko’s suggestion to slip into the principal’s office and retrieve a crucial disk. The sisters soon sense the tension building around this secretive act, drawing them into its unfolding consequences.