Start with Skeleton Soldiers, Upgrade When Killed.

He traveled through time and became a skeleton soldier in the war between the kingdom of the undead and the human empire. He was burned to death by a fireball as soon as he crossed over. Unexpectedly, he activated the upgrade system when he was killed! From then on, others relied on killing monsters to earn experience to level up, but Li Heng—— "I don't know about experience bars, because I upgrade directly!" "Everyone is welcome to kill me!" This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.