After Agreeing to Inherit the Cave, What the Hell Is Upgrading to Become an Immortal?

Yang Yuanzhen was a miserable child. His thoughts were cut off from his brain since he was a child, and he became abnormal. Yang Yuan's family had no way to deal with the headaches that happened regularly, until one day, Yang's mother went out to find a fairy doctor. Three strange people came to the house. Yang Yuan completely misunderstood their identities and thought they were people from the mental evaluation center, so he actively cooperated. But they don't know that they are not human. He signed the contract and inherited the cave of his great-great-great-grandfather. His ancestor was an immortal, so he must be more reliable than the liar his mother found. Also, didn't we agree to inherit the Cave Heaven? Where's the artifact for cultivating immortals? Why is there a system, what the hell is upgrading and cultivating immortality? I am a mortal, and if you ask me to upgrade to become an immortal, and let me interact with immortal cultivators, isn't that nonsense? Oh, I told you earlier that the system of cultivating immortals would be upgraded! Come on, come on - let me try your depth—————— From now on————Upgrade your cultivation to immortality———— This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.