Although it starts up like a silly-ish scare focused haunted mansion deal, when you finally get into an ending it takes form and becomes something quite special that surprised me. Most definitely the origin of both choice-ending based adv/vn (wtc is really inspired by this, presentation and story-wise) and even possibly horror rpg maker games. It's a classic for a reason, and hell, it even made me cry.
Endings completed as of yet: 1

when the 草 切りs the 弟!!!