That is the "magical spell" passed down from grandmother.

One particular summer, Yoshino (main character：Renameable), a 17-year-old girl, follows a butterfly through the main gate.

Beyond the gate, she finds herself in Taisho Era red-light district of Yoshiwara, where the cherry blossoms are in full bloom.

There she encounters Harufumi, a young writer, and Kocho, a male geisha.
Yoshino tries to find her way back to modern times while searching through the Yoshiwara district, where the nights are wild and rowdy ......