Masa appears in nearly every single episode during the first two seasons, and mentions at least once to "Take your calcium!". Masa loves fish, they are definately his passion. He rides a bike throughout town, and wears a funny apron with a fish on it. When trying to talk to Masa about Net Battling, he'll pretend to not know a thing about it. "Net Bath? What is that?"
However, we soon learn that Masa is not all who he appears to be. Masa also poses as the mysterious Net Battler known as "Commander Beef", and is the operator of the Net Navi called Sharkman (big surprise). He also seems to be the leader of an organization called Net Agents, which are geared towards stopping net crimes.
When Masa is not parading around as Commander Beef, he's doting upon the beautiful Mariko-sensei, who is Netto's teacher at school. Unfortunately he has some competition for her affections, the rather nerdy otaku known as Higure Yamitaro. Masa likes to make him continuesly angry by mangling the pronunciation of Higure's last name.