He transmigrates into a book as the protagonist gong's junior fellow disciple.
Zhu Hai says he's fallen for his senior brother, and the first step to winning him over is to break up the canon couple!
With one foot on a demon beast's head and one hand wiping blood from the corner of his mouth, Zhu Hai is very pleased. Great, the protagonist gong and shou won't have the chance to meet now. But why did they still meet?!
After tricking and scheming his way into exchanging a "token of love" with his senior brother, Zhu Hai is thrilled. So why does he spot the hair crown the protagonist shou gave his senior brother on the man's head the very next day? That's a real token of love!
While his senior brother is away, the protagonist shou comes to see him. Zhu Hai makes himself look bruised and disheveled.
"Senior Brother just went out. Sorry, I'm feeling a little unwell, so I can't properly host you."
Watching the protagonist shou leave in a huff, Zhu Hai smiles smugly.
Then he hears that the two of them have gotten together?!
Zhu Hai's smile slowly disappears.
So I'm just a cannon-fodder character used to move the protagonist gong and shou's relationship forward?
Theme: When you like someone, you like them simply because you do. No outside force can change that.