You're a kakuen

A arrow was stuck in the door of the Dojo of Sakonji Urokodaki, Sabito's master.

The old man and his student both know what it mean.

A kakuen, one of these half monkeys man, that kidnap women because there's only male on their species.

Sabito take his katana

“Don't worry Sensei. I will kill this monster.” He goes outside and wait.