
They are soulmates though, this is already established. We already have confirmation that the uke does have the seme’s name on his butt, the uke just doesn’t realise it’s there. Did you not register that from the earlier chapter? It was shown that the uke’s parents just thought it was a birthmark or bruise.

it can be considered a twist and not all plot twist needs to be mindblowing or unpredictable. Sometimes theres a good foreshadowing in the story that makes the twist predictable from the start and youre also able to predict it. I also guessed that the mc is indeed his fated pair before the reveal and that his name tattoo might have been somewhere behind his ear or on his butt haha
I don't know why, but I get the feeling that they are actually not soulmates. I think this because they made a point in mentioning his no-namer friend getting dumped by his namer boyfriend. They also made a point in saying there can't another person with the same hanja name as the uke. And since the seme registered as a namer, I think his real soulmate is someone else.