Arthas fell asleep for four years after wearing the Lich King helmet. What did he do when he woke up? Please elaborate.

When Arthas put on his helmet, he fell into a deep sleep for four years. In his soul, he split a doppelganger representing his only remaining rationality and humanity, a young Arthas. As long as the child is alive, there is hope against evil forces. However, after repeated struggles and games, Arthas gave in, giving in to his inner darkness. He personally destroyed his incarnation of human nature, and filled his chest with frost-like sadness. At that moment, all the regrets, cowardice, introspection and doubts of Arthas were erased, and the once powerful light power was swept away. He completely abandoned everything in the past and became a completely heartless demon. Nerazu's soul was ecstatic. He declared that Arthas would become the Lich King with him, but then Arthas' actions surprised the old shaman, and his sword ran through Ner 'zu's soul: "Not us". No one can tell me what to do. I've got everything I need from you-now this power belongs to me, only to me. I am the Lich King. I was ready for this. "Arthas swallowed Ner 'Zu's soul, seized his power, turned himself into the Lich King, and woke up from the throne of ice. Fragments of his humanity have become an illusion on Northrend, guiding past adventurers to explore the truth-from different directions in the Lich King expansion: Arthas directly destroyed the frozen inner left, and then put on a helmet symbolizing the Lich King to form a new Lich King, not Arthas or the inner left, but their combination.