Johnny is Hiroki Ishiyama's best friend. He is in the same grade as Hiroki and has a big crush on Yumi. He and Hiroki are great locksmiths, as seen in Hot Shower.
He is always trying to think of ways to win over Yumi. In the episode "The Pretender" he got advice from Ulrich to follow Yumi around all the time. Yumi didn't like this at all, and became angry with Ulrich for doing such a thing. But after a Time Reversion, Ulrich got a chance to make up for his mistake, and Yumi and Johnny got along better in the end.