Cultivation: Being Immortal

Lin Jiang travels through the world of cultivation and obtains the Lifespan Check-in System.
Check-in for a day, gain one year of lifespan.
This nearly infinite lifespan allows him to live tens of thousands years, bearing witness to numerous lives passing by, their joy, grief, and everything in between.
He has persisted from the Stone Age to the Cosmic Age and ranges from cultivation to science. He is there, always there, as the eternal guardian of mankind.
(Not a dark and thrilling story, be cautious)