Underflow Glitch to Maximize Friendship Level
This game has a friendship level with each character - in order to get each character's ultimate weapon, that character (although some require other characters as well) must be at its highest level, Excellent. Fighting alongside them boosts friendship, while fighting against them lowers it. However, if the friendship score goes low enough, it will underflow and go from Normal to Excellent. As a note, this bug also works in reverse - if it goes high enough, it will overflow and go from Excellent to Normal.