Ritsuka, a Master from Chaldea, suddenly loses consciousness and finds herself whisked away to Shimousa Province in Edo-era Japan. But it soon becomes clear she's not in her own timeline...and neither is her companion, a woman called Miyamoto Musashi. Together, they must defeat the Seven Heroic Spirit Swordmasters, a group of fearsome cursed warriors who will stop at nothing until every living thing on the planet is dead.