The Story of Killing Demons and Immortality

This is a world where killing demons can lead to longevity. The protagonist unexpectedly gets a memory of ten thousand years and begins to hunt for treasures by killing demons. I got the Immortality Tower on my first treasure hunt, and I was one step closer to immortality. Kill the little demon for twenty years and gain a hundred days of longevity. If you kill a little demon for fifty years, you will get two hundred lifespans. There is a chance that you can get high-quality demon cloth, which is about the size of a palm and can be made into clothes. If you wear it on the human body, it will be invulnerable to all poisons. The ten-thousand-year-old demon wants to be a grown-up, and he also wants to live forever!