Lifespan Is Exchanged for Power, I Have a Demon-Suppressing Tower

[No system, traditional fantasy, longevity, decisive killing] Traveling through the world of cultivating immortals, you get the Immortal Body at the beginning. During the chase, you accidentally get the Nine Heavens Suppressing Demon Tower, which is full of evil cultivators who want to die. "Five years of longevity in exchange for a holy magic weapon, the Star-Destroying Demonic Sword!" "Ten years of life in exchange for Tianxuan Chanting Sutra" "Fifty years of life in exchange for Ten Thousand Thunder Body, Lei Yuan Jue!" … Lifespan exchanged for power, am I invincible?