beta
The og Yuu is the eye blob and the og Mika is the Angel, at some point their souls swapped bodies. So now the one we've come to know as Mika is the og Yuu and the we've come to know as Yuu is the og Mika. They swapped because of some bullshit that was "kinda" explained in one the more recent chapters, but I'll do my best to explain.
After Sika's punishment by God ended he tasked the og Yuu to make dolls that would be "human" and was shoving dead angels in them. One of those dolls had gone up to og Mika's body to find that the og Mika was still stuck in there and gave his body to him. Tbh I don't know what happened to that guy because there was obviously another dude in there but the implication is that he's completely gone. Since right afterward og Mika is clearly shown doing all the talking with 100% control of the body. So I think the og guy got sent to the void???
Then they both formulate a plan to try and keep Sika Madu safe by making it impossible for him to revive og Mika. So right after that og Yuu puts himself in the old Mika's body and explodes it to hide the seven keys. Og Mika makes a promise that he will always find Yuu and that from this moment they'll always be one. (In the sense that they will will always be together and that their destinies are now one)
The og Yuu is the eye blob and the og Mika is the Angel, at some point their souls swapped bodies. So now the one we've come to know as Mika is the og Yuu and the we've come to know as Yuu is the og Mika. They swapped because of some bullshit that was "kinda" explained in one the more recent chapters, but I'll do my best to explain.
Long story short and to clear things up this not selfcest. There are still 2 souls and involved and they were never the same person.