Narifumi Hosokawa works with the Kadomori twins, Shizuku and Kasumi, to prepare for his high school’s culture festival. While everyone is busy, Shizuku decides to use magic to unlock a mystery portal and journey to another realm. She has betrayed her family’s pledge to protect the Black Gate from those seeking the immense power that lies within the globe. The Black Gate’s remaining defenders, a group of female pupils and a female instructor, must journey to the other side and return before any disturbances occur in either dimension. Narifumi, on the other hand, is with the group, and Shizuku is waiting for them with some new pals.