What if you add like a feature in the Diary option to see the statistic about your game progress? It's a Diary after all, it's supposed to have noted everything you do. Maybe in a system that counts like how many items you've found and how many are there left that you haven't discovered yet (weapon, armor, potion recipe, or something else), killing count for what type of enemy have you killed and how many are they, random event that you've encountered (like the speed potion recipe encounter, its kinda important and you can miss the encounter right? why not add it into a diary then), also an ending counter (I remembered you say something about the game have different endings, would be fun to know how much endings you've got in case you forgot and how much more endings you haven't gotten yet), and how about a monster encyclopedia? Maybe you can add a description to every enemy you've fight, like a backstory or enemy appearance description, maybe even a note about its weakness if you're planning on adding that later.
The Diary option seems kinda empty right now or at least I think so. Would be great if you add something to it to brighten it up!