▁ 5 9 5 9 ▁In ▁July ▁ 2 0 1 7 , ▁J elly fish ▁Entertainment ▁formed ▁the ▁sub unit ▁group ▁named ▁G ug ud an ▁ 5 9 5 9 ▁( ; ▁sp elled ▁as ▁" O gu - og u "), ▁composed ▁of ▁the ▁young est ▁members ▁M ina ▁and ▁Hy ey e on . ▁The ▁" 5 9 5 9 " ▁name ▁is ▁made ▁up ▁of ▁their ▁represented ▁numbers ▁in ▁G ug ud an : ▁Hy ey e on ▁representing ▁the ▁number ▁ 5 ▁and ▁M ina ▁representing ▁the ▁number ▁ 9 . ▁ 5 9 5 9 ▁released ▁their ▁debut ▁single , ▁" I ce ▁Ch u ", ▁on ▁August ▁ 1 0 , ▁ 2 0 1 7 . ▁ ▁After ▁Hy ey e on ' s ▁departure ▁in ▁October ▁ 2 0 1 8 , ▁the ▁sub unit ▁consequ ently ▁became ▁in active . ▁ ▁G ug ud an ▁Se M i Na ▁ ▁In ▁June ▁ 2 0 1 8 , ▁J elly fish ▁Entertainment ▁formed ▁the ▁second ▁sub unit ▁of ▁G ug ud an , ▁composed ▁of ▁members ▁Se je ong , ▁M ina ▁and ▁N ay ou ng , ▁named ▁G ug ud an ▁Se M i Na ▁( ). ▁The ▁" Se M i Na " ▁name ▁is ▁made ▁up ▁of ▁the ▁first ▁sy ll ables ▁of ▁the ▁members ' ▁names . ▁G ug ud an ▁Se M i Na ▁deb uted ▁with ▁the ▁release ▁of ▁their ▁self - t itled ▁single