
My imagination is getting wild (not in R18 way, not entirely) with this kind of story. But I keep on having theories, what if it is their past? What if Sungwoo write the book base on what really happen to them in the past . Arr can't explain it clearly. ┗( T﹏T )┛

Read here, Chapter 16 on this site https://genkan.io/manga/9216430884-a-casual-friend
The best friend is the end game and I won’t accept any other opinion