Dick's obviously had plenty of martial arts training... but never with any edged weapons beyond his batarangs. Bruce was always pushing him to keep learning, to making sure he didn't accidentally calcify to one specific fighting style and find himself in a situation that his acrobatics and hand-to-hand might fail him. So why not take a look at kendo, right?

At the very least it would help him keep in shape without people questioning his drive.

He approaches Hijikata with an open smile. "Hello, sensei. I didn't sign up during club week."