You have to save Suzuna. You can buy her for 5m.
You have to visit her room.
You have to read 3 books in the bottom of the Dwarven Library. I wanted to attach an image showing which books but this site won't let me. Here's a link ->
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You can read the same book three times for the same result.
Defeat the white knight (last boss), go to the Front Desk, Talk to Hood. Get the Repair Item from the chest in Front Desk. Go get the book repaired, read it. Go to the thrown room, go to the back and to the right and get the princesses journel. Read it and get cut off by someone. Go to your room and read it again.
Go to the end of the game, enjoy the ending. I laughed. The facial expression was priceless.