All the male leads are adults from the very beginning!
This is a story about a System making a straight man forcefully pursue and claim a top, while the straight man thinks he can be the top. In the end, he's forced to become the bottom.
[A bottom who keeps thinking he can be the top and flirts everywhere ✖ a seemingly innocent but secretly sinister top]
To complete his mission, Yan Xun flirts around and drives away everyone close to the top. Everyone knows the illustrious reputation of Young Master Yan, and Yan Xun has always believed he is the top.
After shamelessly trying forever, he finally manages to make Shi An fall for him. Yan Xun, a straight man, only knows how to flirt and never considers the consequences. But Shi An really does fall for him. Just as things are about to heat up, Yan Xun realizes he is no match for him. He gradually sees that this isn't the bright, moonlike youth he first met at all, but a demon. Terrified, he makes a run for it.
But fate takes an unexpected turn. Shi An is harmed, and Yan Xun thinks that even if Shi An recovers, he'll never be able to be the top. Believing he can finally turn the tables, Yan Xun doesn't realize that this time Shi An has no intention of letting him run again.
Yan Xun, weakly: If I had another chance, I'd never flirt around again. I'd definitely take a detour whenever I saw Shi An.
Good-looking, good-looking, good-looking