After traveling to the plane of the undead, Aku became the lowest skeleton soldier. Faced with a world of bones where life and death are entangled, where the weak and the strong prey on the strong, he decisively chose to lie down - until he discovered that he had an outrageous talent: by sacrificing his own skeletal parts, he could forcibly enter into a master-slave contract with any undead.
So, he silently picked off his ribs and replaced them with half a soul crystal; he took out his finger bones and replaced them with rotten apples. He relied on "selling off his property" and grew up on the edge of his territory. He exchanged bones for strange materials and accidentally "bought" more and more undead "creditors".
When the Lich Lord's army pressed forward, demanding a hundred years of tribute, and all the undead souls were trembling, Aku took out a stack of contracts full of handprints - the names of the Skeleton General, the Bone Dragon, and the Blood Queen were clearly signed on them.
"Lord," he shook his body with only the skull and spine left, and asked slowly, "Now, is it your turn to pay the protection fee?"
