Yoon Seo-yeon, more commonly referred to as simply SeoYeon, is a South Korean singer and dancer under MODHAUS. On May 1, 2022, she was introduced as S1, the first member of the 24-member girl group tripleS. Yoon Seo-yeon, more commonly referred to as simply SeoYeon, is a South Korean singer and dancer under MODHAUS. On May 1, 2022, she was introduced as S1, the first member of the 24-member girl group tripleS.