The game features a custom character system that allows you to transfer your character from game to game. You can edit your character's description, and the AI will use it when interacting with you.
There's also a NPC memory system, but it's based on dialogues during the game. However, you can import them into a new game.
For now, this is all I have. I remember asking about the possibility of editing the initial data for NPCs, but as I understand it, it's easier to edit them manually in the note field in the dialogues.