Because those are 2 different people.
Huh??????
If you asking about the panel where he’s kissing in the classroom, the artist has drawn the mole on the wrong side!
Not in every panel. In regards to the classroom scene, I think it was just to show that it was the seme kissing the step-brother,
Which this was just in the first chapter.
STEP BROTHER?
Why are his moles placed differently every panel?:(