Koga Yudai (古賀 祐大; born October 21, 1997), known professionally as K (ケイ; 케이), is a Japanese singer and choreographer under HYBE Labels Japan. He is a member of the boy group &TEAM. Koga Yudai (古賀 祐大; born October 21, 1997), known professionally as K (ケイ; 케이), is a Japanese singer and choreographer under HYBE Labels Japan. He is a member of the boy group &TEAM.