Either the flow of time here is different from the outside world. Even in the Nirvana Realm, no matter how powerful they are, with Blood Rebirth, they still have only three thousand years of lifespan. Once that lifespan is reached, without achieving Wanxiang, one will ultimately sit and transform.
What, then, is truly eternal? No wonder all the cosmic powerhouses enter the Star Ruins Realm.
In the Sitting and Forgetting Realm, even if one has reached the Forget Realm, it is said that space can be opened, and one can be immortal as long as heaven and earth are immortal. Yet, heaven and earth will eventually decay as well.
In the Cang Mang Domain, above the Vientiane Realm, lies the Chaos Hole Realm, but even that realm does not grant tens of thousands of years of lifespan. They might seem omnipotent, acting as Supreme Sect Leaders, masters of a sect, but how long can one live here?
