What would happen when one day you are suddenly confronted with a realization that you cannot afford to see someone get hurt?

Masked with white lies to keep Jimin’s smile, Minjeong brought herself to do what Jimin’s ‘supposed-to-be’ girlfriend should be doing for her.

The promise of just being with Jimin's side through cancelled dates began to morph into Minjeong writing letters for the girl in her best friend's stead. 

Or to put it simply,

Minjeong couldn’t afford to see Jimin get hurt when her own best friend, Ryujin fell out of love for the girl. Hence, she did stupid (or maybe not) things for the latter.