That's because you guys are playing the "free version"; it's only available in "paid full version"
Hi, I just finished it, and think maybe that "file 8" is meant to be blank? I have played the others, which "khywae's boat" is always at the last file (even with some previous blank files - which awaiting my selection of other choices for them to appear), so since for Toji's, boat is at "file 7", that should be the end; maybe khywae just somehow set one additional save slot that is not used for this game, ^ ^