
so why after all the 5 lives she had been, the emperor decided the MC is shasha now???

Most likely because of the second heart he gave her after he almost killed her even though he knew she isn't his Charlotte. He practically imprinted on her and now wants her to have his child as that's how it works with this story's concept of the golden dragon. He forcibly in a way claimed her as his breeding ground as he can't have children with anyone else but her.
is that really isaac like...thats not him isnt it?