“Brother, I like it.” “Brother, I love you.” An immature seventeen-year-old Goo Yeol-ae who fell in love with her friend's brother, Choi Kang-guk, and passionately courted her. He devoted 10 years of his life to being honest and sassy. Now, twenty-seven, I'm more hungry for love than to give... … ! Still, the strongest country is the strongest tsundere man. At a time when change was needed, they squirmed on the front of their love. Goo Yeol-ae, who got drunk and attacked Kang-guk's room, was found in Kang-guk's bed the next morning! 'If it's not the mind, I'll take the body.' A woman whose conscience worked, declared. “Brother, I’ll let you go. Instead, just stay with me for one night.” “Only once.” And, the promised night... … she has arrived Will the devotees be able to set a strong country? Maybe it's the huge design of the devotees who want to realize the rule of law, such as the effect of one night? Can I catch the strongest country, the '10-year unrequited girl' I want to be a devotee rather than courtship, and the 'strongest tsundere man'?