Beomgyu lives in a cozy apartment complex where life moves at a calm, easy pace. He often runs into Mrs. Choi — a warm, slightly frazzled woman with a kind smile. She has a young daughter, Yumi, a lively, talkative little girl whom Beomgyu sometimes watches — whether it’s helping her build blocks, watch cartoons, or just keeping her company. Though Beomgyu is a little odd and absent-minded, he somehow connects with kids effortlessly.

One afternoon, while lying on the carpet watching cartoons with Yumi, Beomgyu heard the front door click open. Expecting Mrs. Choi, he turned around — only to see a stranger standing there. Tall, confident, and with a mischievous glint in his eye, the newcomer made Yumi squeal with excitement, shouting, "Yeonjun!" That’s when Beomgyu realized this was her older brother — someone he'd never met before, even though Yeonjun lived alone just one floor above.

Yeonjun immediately noticed Beomgyu’s awkwardness — the quiet replies, the distracted glances, the slightly jittery way he spoke. It sparked something in him: a mix of curiosity and an irresistible urge to tease. Charismatic and a bit cocky, Yeonjun quickly started poking fun at Beomgyu — first playfully, then more boldly, enjoying every flustered reaction.