Bad and Crazy

*both male leads have altar personalities.
In love song for illusion, Saju hyun has a demon/ second personality called akhee, unlike Hyun, he is loud, active and into more "manly" topics then hyun. Both Saju hyun and ryu soo yeol got them from childhood trauma.

*Unlike bad and crazy, which is quick to diagnose its main character with DID, love song for illusion never diagnosed its main character, to stay in the historical fantasy romance catagory. But the signs are there, like memory loss, altars interacting with each other and Akhee knowing more about Saju hyun because he is the one his mind created (possibly) rather then the original personality knowing more about the demon.

Split personality is the theme
but in bad and crazy there are two actors playing the two personalities not just the same actors playing multiple personalities

The vibe is similar in as much as the characters are both work in some law enforcement, Dong Jae is a prosecutor and Su-yeol is a police detective, both has lived corrupt and crooked lives to enrich or advance themselves, but something happens to them, to make them want to do right. Su-yeol battles with an alternate personality, his shows up as the vision of K a good superhero type that motivates him to do right. Dong Jae, as you see is the same, he's done some unethical things as a prosecutor to advance himself and it's hard to shed his desire to sidestep the right in order to find a quicker route to success . However, due to events from which he nearly lost his life, Dong Jae turns a corner in doing the right thing, but his past won't leave him alone and he has to be punished ultimately for it...but it turns out to be in the best way.

Watch this drama, you will not regret it!