Osamu Watanabe is the coach of the Shitenhōji tennis club. Watanabe reminds us of a younger (and hipper) version of Yamabuki's Banda Mikiya. Like the latter, the former's interaction with his students is very laid-back, often shown joking around with them. Watanabe is also pretty sly. When the team first learned of Chitose Senri's resignation, Watanabe appeared ambivalent about the issue.