They met when they're young, MC helped ML when he's having a hard time of the poison on his body, He just know that the one who helped him name was Song Song. Thought the child was killed cause of him but later he know that the savior still alive and will be wedded to him. MC already in ML's heart

For ML it's hard to control his violent impulses even when he's aware. But he never assaults MC. It's like wanting to smash your annoying brother's head with a plate, but you don't actually do it because you don't want to hurt him? ML can't turn off the switch once it's on. ML can control his bouts of crazy only with his feelings for MC. Maybe if his mom is still alive she can help ML too. Though a bit unrealistic, I love this plot device.

I was surprised ML was not getting cured over time. Only his self control is getting better, he's still a mentally ill patient until end of series. Maybe because he doesn't think normally, 1) he keeps not talking about their rebirth-thing to Song Song. 2) he's so flippant about calling himself emperor in his crazy spell. 3) he talks like he's a bit dazed sometimes, fixating on one thing and overthinking. 4) he even gets jealous over his own son.

ML also has a wrapped sense of most things. Rationally he knows that MC loves him but can't convince himself that MC who never lost his calm loves him like he loves MC. ML will always follow up by explaining patiently what sort of relationship he wants to have with MC, multiple times, explicitly.

At the start Song's reluctant to misuse his favor. And ML doesn't say outright that he knows what happened in last life (1) so MC treats ML courteously at first. Then, he slowly becomes more spoiled and relaxed with ML, it's cute hehe

Since both MC and ML have reincarnated they are dedicated to each other and there is no major misunderstandings. They just both know what they want, and spoil each other rotten. They are both each other's salvation on a way.

It was so funny when the ML wanted to see the MC angry. He touched the MC's bottom line when he pretended to not be able to speak and hear due to shock. The MC was so mad he kicked out the ML and refused to talk to him and made him sleep on chairs instead of the bed. It was so funny because it was totally the ML's fault. Then the ML realized that he likes the docile MC more because he would suffer so much if the MC gets mad again. Lol.