I have a few Opinions so I'm just gonna attempt to list them clearly
1) I don't think Emperor is the ML cause that's just fucking creepy
2) They actually might be related in some way. the most common theory, that Seriah being her mom and Emperor being her dad but think of this, Seriah and the Emper didn't know each other prior to this as we know of. So unless we get more intel on that the theory is no go