More than 100 people filed into a small cafe in Seoul's Hongdae area on Sept. 12 to celebrate the birthday of Felix, a member of K-pop group Stray Kids. Felix was not there. No one expected him to be. The event, known in Korea as a birthday cafe, is far from rare. In Hongdae alone, nearly 100 happen every week. Not all of them are for idols. During our visit, cafes across the neighborhood were also celebrating animated characters and virtual YouTubers. For Korea's coffee shops, the trend has become a lifeline. The country had 107,055 cafes in 2024, and the number fell for the first time in early 2025 as profits came under strain. In a market that crowded, a fan event guarantees what owners struggle to buy: customers. The math The arrangement is simple. Fans rent an ordinary cafe for several days and promise the owner a minimum number of sales. Felix's organizers committed to 350 drinks over four days, at about $5.50 each. "The owner takes everything from the drinks," said Choi I-su, 44, one of five fans behind the event. The organizers pay for decorations and free gifts themselves. Their