There were a few novels in which the protagonists 'cultivation was obtained by trading their lifespans. They were " Controlling the Heavenly Book of Longevity at the Beginning "," Lifespan Recharge System "," Longevity: Selling Lifespan to the Devil, I'm Invincible "," Krypton Warrior Sage "," The Strongest Trader in the City ", and " Rise Begins from Trading Lifespan ".