A story about a childhood friend's kunoichi being cuckolded

The hero, who dreams of becoming a kunoichi, is finally hired by a certain castle.
He says goodbye to his childhood friend Musashi and leaves the village where he was born and raised,
The men who live in the castle and castle town are a bunch of perverts.
Musashi is drugged with aphrodisiacs, and as his body is developed, he too is hired by the castle to work as a samurai..,
He is hired by the castle to work as a samurai...
Musashi is not allowed to know that his body has been developed...
Can he survive as a kunoichi without being exposed to Musashi's body?