In a world teeming with monsters—妖兽, 恶 魔, 天使, 巨人, 精灵, 幽灵,妖精, 女巫,兽人, 虫族—countless races and endless mysteries, humans can sign pet beast contracts. This is a story of taming, nurturing, advancing, evolving, mutating, and battling these creatures. Evolution examples include: Mud Giant to Black Iron Giant; Small Flame Sparrow to Gilded Flame Bird; Four-winged Angel to Six-winged Dark Angel; Demon Ape to Eight-armed Evil Dragon Ape; and more.