Thanks so much for playing all the way to the end, hope you enjoyed! I thought about doing a walkthrough and still might -- if you get the ending gallery it does tells you more or less how to get all the endings.
You get the passwords from four specific endings. Spoilers for where to find all four passwords under the cut:
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1st password: lose Rose's game.
2nd password: fight the hero without the mimic's treasure.
3rd password: skip breakfast with Thea and then play through to the end of the game.
4th password: get the true ending.