blondie being in the story give the readers awareness of pedophiles and freaks out there who keep pestering innocent & guilible minors. seunghee is one of the most realistic high schooler I've seen in webtoons so with the blond guy, he could at least know some boundaries & can be more aware of freaks around him.
he's in high school, he still needs to LEARN in life & he makes mistakes too
in some stories, having flings/a thing with older people are considered normal & authors didn't point it out properly on what's wrong about it but this one actually points it out clearly