Forgotten Intimacy

Kyungsoo, Areum, and Kai. All childhood bestfriends. Kai and Areum dated all throughout highschool until the incident happened. 5 years later and now Areum's with Kyungsoo while Jongin has grown away from them.
After an accident, Areum is lucky to have survived, but she does not exactly remember everything. . .
Hopeful, Kyungsoo asks Kai for help: get Areum her full memory back. But while helping out an old friend, Kai begins developing old feelings for Areum.

Now it's back to square one.