Lin Shuyin is a ghost with a mountain of sins. According to the laws of the Underworld, he should spend at least another five hundred years frying in the oil cauldron to cleanse his sins before entering the cycle of reincarnation again.
But Lin Shuyin can't stand suffering. He couldn't endure five hundred years in the cauldron, or even three days.
So when an Underworld administrator found him and said that if he went back in time and killed his former self just before he turned evil, he could return to his body and come back to life, Lin Shuyin agreed at once.
He couldn't use his real name around his younger self. But Lin Shuyin was no decent person, and he didn't even spare his past self. He told the young Lin Shuyin his name was Shushu [Uncle].
Little Shuyin believed him and called him Shushu all day long. Lin Shuyin loved hearing it, so he took even better care of Little Shuyin, all the while getting ready to reclaim the right to use his body.
When Little Shuyin was locked in a dark room by his parents and given no food
Lin Shuyin brought him food: You need to eat well and stay healthy.
[That way, the body he'd get back would be strong and healthy.]
Little Shuyin: Shushu, why are you so good to me~
When Little Shuyin was bullied and kicked around by his classmates
Lin Shuyin rushed out to take the beating for him: They can hit me, but they can't lay a finger on you.
[This was the body he planned to use later. He couldn't let it suffer any lasting injuries!]
Little Shuyin: Shushu, you're the best Shushu in the whole world~
And so Lin Shuyin earned Little Shuyin's complete trust. Then, on the night Little Shuyin was about to confess his feelings, Lin Shuyin took over his body and happily began his reborn life.
But this wonderful, comfortable life lasted only a few days before the vanished Little Shuyin returned, now a Ghost King feared by all three realms and six paths.
Ghost King Shuyin: How are you going to repay what you owe me?
Lin Shuyin: I'll let you use this body?
Ghost King Shuyin: Fine.
Later, on a dark and windy night, Lin Shuyin clutched his aching lower back and regretted everything. I said you could use this body, not use me!
Ghost King Shuyin: Let's leave it at that. I'm quite satisfied.
Lin Shuyin: Sob... Help... I'm exhausted...
PS:
1. Narcissistic romance.
2. The plot exists to serve the romance. Logic has been fed to the dogs. If you argue with me, you're right.
Theme: You will always be your own strongest support.