Michael and Lucifer are supposed to be twins in Makai Ouji, right?
When it comes to actual twins, there’s always a stronger and a weaker twin, due to there not being enough ‘food’ for both the growing children in the womb and all.
We’ve never seen Lucifer’s face, he’s always partially covered by his wings and feathers. That gives me the indication that he’s the weaker twin. the only issue Michael has is that he’s been too long without sleep, other than that he is definitely stronger than Lucifer.
That makes me think that Lucifer isn’t as bad as Michael makes him out to be. Michael simply tries to antagonize Lucifer who is, despite sleep, weak, probably constantly.
That’s just a theory, but it’s how I see it. what’s more is that I think Lucifer held a lot of feelings for Solomon. It doesn’t matter to me if they’re possibly romantic or not, but they clearly had a close bond.
The demons thought they needed a new King, a second Lucifer, until William put the ring on and Solomon awakened within him. Lucifer rose once more then, and most likely told him to leave that poor young boy alone, if that intimate touching William/Solomon did to one of Lucifer’s fallen feathers and simply said “I understand” before disappearing.
I think Lucifer realized there is a significant difference between Solomon and William, and wished for Solomon’s conciousness to leave William alone. Why that is, I can’t answer. but I think Lucifer is a good guy.