This story tells the love journey of Kim Sejeong, a staff sergeant in the Korean Army, and Jeon Somi, a famous k-pop idol. Covering the mystery, betrayal, hidden mission, and hardship behind their love story and also how the other ioi members take part in it. Jeon Somi, Choi Yoojung, Kim Chungha, Kim Sohye, Zhou Jieqiong, Jung Chaeyeon, Kim Doyeon, Im Nayoung, Yoo Yeonjung as IOI members Kim Sejeong as Staff Sergeant in Korean Army Kang Mina as Kim Sejeong's half siste