Grindiok the Stoneball Mason is a minor entity of the series of the Battle Day/Exchange Student Zero Saga.


He is Hiro's former rival when it comes to boards. Following his defeat, he swear to beat him, the next time they meet and gain Champion's Board he most deserved.


Hiro Karuta

He has long grudge against Hiro since his defeat on their battle. Believing he was cheated, he waited until the day Hiro will use the board and get his rematch.

John Stitt

He had a short feud with John, when Hiro refused to battle him and instead the faced off with the new user of the board. None of them won, but surely got to endure the most injuries.


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  • His card is from the Roller Clash Expansion.
  • His Appearance is based loosely on Proto man from the Mega Man series.