Kihon only remembers
Kihoon forgot everything. Yeon is the only one that remembers. Yeon feels immense guilt for what happened in their past life and know that it's technically his fault that Kihoon was plagued by misfortune and went through so much hardships. And even in this life, the misfortune continued. Even though the quests cleared all the misfortune, Yeon didn't want to burden Kihoon even more. So he asked Kihoon to forget him and Kihoon, the lovesick fool he is, chose to listen to Yeon and forgot all of their shared history.
I'm wrong
Is kihoon the only one that doesn't remember or did they both choose to forget???