Dual male leads
He never uses brute force to take what he wants. Instead, he uses his frail constitution and gentle appearance to manipulate his mission targets, one step at a time. He uses “playing weak, dependence, indulgence, and tenderness reserved just for you” as shackles, slowly trapping the obsessive love interest until they can't bear to be apart from him.
It looks as though the other man is the one being clingy and assertive, unable to live without him. In truth, he controls the relationship from beginning to end, gentle XX and possessive to the last. He's the quintessential frail, seemingly innocent but secretly calculating top.
First person, the rest is almost the same as the introduction