Ganghis Khan is the eldest son and general of Garaiya, and also the one who first discovered you can absorb the soul of those you kill, which also absorbs their magical affinity. Ganghis uses this to kill Belle right in front of her brother Griffon and absorbing her insanely realized magical power of grass, and in-turn, stealing her eternal youth and twisting it to revert himself to the prime age of his own power.
