I actually completely based him on a character from my Blue Flame Saga. His name there is tentatively "Calm" (because I don't know how I feel about that name). The look is almost identical minus the Cloud forehead protector on his arm, er, and plus a few features on his jacket, actually. Calm also has some major disabilities that I didn't give to Shizumaru, but I might've actually given those to Calm later.
Shizumaru had a big thing where he basically always kept his eyes covered. He'd only reveal them as a threat, for some reason. I planned on him being a Water and Lightning Style combination expert. I always imagined him combo-ing Water Prison and Chidori, though Water Prison wasn't something he'd have easy access to learning, as it was a Kiri secret technique, and he was from Kumo.