You're trapped in a hot springs in with your big titty kouhai. Until you find a way out, I guess there's no other option than to get lovingly squeezed between her 137cm breasts.
This game has some classic horror game elements, where you find lots of clues and objects and use them to gradually work your way to escape. As you learn more about the lore, you inch ever so closer to the goal. Progressing through the main story isn't terribly obtuse, though sometimes you'll find yourself stuck because you didn't realize you can actually travel to certain areas. In addition to needing to hop over the reception desk, there's also a ledge at the top of the Main Hall where you need to hop onto to get a crucial item to proceed. Be sure to Talk to Kouhai if you're feeling stuck, as she'll provide items and even the answers to some puzzles if you've gathered all the necessary clues beforehand.
Besides the main quest, there are also items that lead you to getting a second ending. These clues are going to be more obtuse at first, but progress through the story and maybe things will become more clear. And of course, you can always lurk the comments section if you're absolutely stumped as our wonderful users work to figure out the game.
It's a short romp lasting about an hour depending on how long it takes you to figure out all the clues. There are also a dozen or so H scenes, all of which are paizuri only. Considering the content and the spooky vibes, I think this is a game that at the very least is worth giving a shot and paizuri lovers will fall in love with for sure. There are some hiccups with the gameplay but otherwise it's not overly frustrating and rewarding considering the game's size.