A mysterious person of Kaito's childhood who had served as something of a master to both Kaito and Rook. His real name is later revealed by Rook in episode 13 from 1st season. He once was kept captive by the P.O.G.

Years ago, Jin contracted with the Orpheus and became a solver for the P.O.G. However, one day, Jin received a vision of the future, showing the world being destroyed by Pythagoras. Jin quit P.O.G and went into a journey to fight Pythagoras in the Puzzle of God. The results of the fight remains unknown.

The origin of his name comes from "魔方陣, Mahoujin" (Magic square).