Gamera - an old Japanese movie monster.
It's unclear whether or not Gameru is meant to be the same giant turtle mentioned in strip . The sizes mentioned are not consistent, though that doesn't necessarily mean anything since Gameru is said to be different sizes in strips  and .
One possible pun with Gameru's name is that final u sounds in Japanese are often mostly silent, leaving "Gamer". That is, unless you overanalyze it:
the readers who don't know Japanese get the joke better than people who do...