Demon Slaying: Start with Krypton Life

You can become stronger by spending money.

Su Ying, who died accidentally, traveled to a world full of demons and evil spirits.

As long as you kill a living being, you can absorb its lifespan and deduce the martial arts infinitely.

A few years later...

The human race actually joined forces with the demons and evil spirits, pointing at Su Ying and cursing: "He's going crazy with killing! Who will control this killer god?"