This is a theory not spoilers but he's gonna have a totally valid reason for skipping school. Youre right that it seems out of character for him but watch I bet next chapter it's gonna be revealed he skips school to take odd jobs so his mom doesnt have to work harder from the credit card seme gave him
That would make sense, but from a storytelling standpoint, it's kinda irritating that the author is keeping whatever reasons he has from the readers.
I mean, suspense? Authors who tell the reader everthing make for boring stories
I don't think this is achieving the effect of suspense, it's just making Sejin appear inconsistent.
This is not making a lot of sense, Sejin wants to make his mother happy in one chapter, and in the next he's skipping school.