To become an Immortal, there are three steps – cultivating to the peak of the Transcendence Tribulation Stage, passing through the Immortal Ascension Tribulation, and transforming all one's Spiritual Energy into Immortal Power.
The Immortal Ascension Tribulation cannot be passed quietly. One cannot cross the tribulation in just any secret place. If the secret place does not have the right position, the Immortal Ascension Tribulation will not descend.
Immortal Power is definitely manufactured from Spiritual Energy, but no one knows exactly how it is made. This is the basis for the existence of the Immortal Realm. It is impossible for long-living immortals to know.
"Old Buddha, tell me, how did you become an immortal?"
The Old Buddha's light is restrained, his flesh is full, he has a lifespan of ten thousand years in the Transcendence Tribulation Stage. He should have been old, but now he seems full of vigor, as if he still has a lot of lifespan left.