Sei Tominaga

富永セイ

aka Kamiya Seizaburo (神谷清三郎)

She disguises herself as a boy to join the Mibu-Roshi, also known as the Shinsengumi, to avenge the murder of her father and older brother. She trains under Okita Soji and develops a crush on him, but also desires to be a true warrior. (adapted from volume 6: US edition)