Benten is the Goddess of Mercy who bares a sword for dragon-slaying, & Kozo means Kid or Boy, so the title literally means "Goddess Boy."
She is cast as a combination wakashu (young man, frequently implying homosexual youth) & onnagata (female impersonator) named Kikunosuke, Kiku for short. Kiku is capable of going back & forth between genders, in one moment speaking like a highborn young lady, in the next like a street ruffian, with tattooed shoulders to prove his street credentials.
Orphaned Kiku was raised at a Buddhist temple & learned theatrical arts & martial arts as a child, which were used to put on stage productions to raise money for the temple, but also to display young lads who were essentially for sale to the highest bidder. As the film opens, Kiku is on a stage performing a Noh "red lion" dance, & a potential customer is at that moment sending money over to the priest's seating.
He is falsely accused of murdering Lady Okugata, to whom he was being pimped by a vile priest at the corrupt temple, a priest who took in orphans then when they're about to come of age sells them to the temple's wealthiest donors.
Benten Kozo,now a young teenager, it was time to make some real money off Kiku, but he balked at being forced to sleep with "the old lady with too much make-up." When the wealthy matron is killed, the angry priest automatically blames rebellious Kiku.
Struggling against bitterness, Kiku goes underground as the thief Benten the Kid, in order to fight villainous gang members, finding a home among young heroic outlaws.