... I thought this was a spin-off of the demon summoner who lived in the rabbit town...
in the 2nd game, https://nomnomnami.itch.io/friendly-bunny-mochi right after you leave the house for the first time, go instead to the house above the store...
She appears more over the games, and I believe she is the one who mentions the train even going to the nether world.
if you have not tried to enter every house at each interval of the game, and/or go to places you did not need to... I will simply say that the original series had quite a few secrets for people who loved exploring that had nothing to do with gameplay... also, at some point there was different dialogs for repeat interactions... so I have no confidence that I found all the secrets.