Because life. Most people are annoying. They make the story more realistic.
for plot progression ? that's how stories work.
You're right
But I never find another man who try to sabotaging my relationship like this sunbae of the seme
maybe this only happens for good looking people who have 9/10 looks?
So I'm not good looking hmm（￣へ￣)
Like what everyday reality for good looking people?
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Why Korean story always have annoying side character
They're not necessary will make the story better