Benkei is a new character who makes his debut in the The Ring of Sky.
He is a master conjuror, being able to make things appear out of thin air and deceive people with his tricks. He calls Jack "nanban" when they first meet.
The Ring of Sky
Jack first meet Benkei towards the beginning of the book after he has been shipwrecked. Jack is running from a group of Samurai who want the reward which is being offered for Jack, whether he be dead of alive.
Jack pauses for a moment and sees a head on the sandy beach, at first he thinks it's a decapitated head, the remains of a samurai who has commited seppuku but then the head speaks and Jack realises that it is in fact a boy, buried up to his neck in sand. He introduces himself as Benkei, calling Jack and nanban. After some negotiating on Benkei's part he convinces Jack to dig him out of the sand which Jack does.
Benkei then promptly leaps to his feet and runs off, Jack in hot pursuit.