You can Reroll the Tensura king of Monsters by deleting game files or binding several emails are the only methods for re-rolling, other than directly uninstalling and downloading the game. It is strongly advised, however, not to re-roll because the rarity of units does not explicitly fit stronger units. Not only is the present summoning pool very limited, but the only character ranked by the SS (0.25% chance of pulling him) is actually weaker than a character ranked by the A who performs a similar role.