Youngin, Se-eun, and Yoon each hold a secret they cannot share with anyone. For Yoon and Youngin, who loved the same person, the past is nothing but a painful scar. Youngin, who lost everything to a passionate first love, and Yoon, who betrayed a friend blinded by selfish desires. And for Se-eun, who wants to heal her friend's painful past, 'Inyoung' is each person's sweet lie. Se-eun fabricates a diary for the happy ending of Inyoung and Youngin... "Han Youngin, let’s play fair, humanly speaking." "Why should I?" There was no sign of retreat in Youngin's eyes, tightly clutching the diary. Although it was a situation she had anticipated, Se-eun was taken aback by the more intense reaction than expected, and she mediated between the two by proposing a few simple rules to organize the situation. The key will be owned by Se-eun, They will read it together, They will read it while accompanied by Se-eun. Youngin and Yoon reluctantly agreed. The diary might be split in half. Se-eun and the two were exactly 50-50, with not a single bit more to add to their fair relationship. Satisfied with the obedient change in attitude from both, Se-eun slowly opened the diary. Everyone held their breath as they gazed at the densely packed words on the untitled background, which had not a single line drawn on it.