...Iru! (...いる!) which roughly translates to "...something’s here!", is a first person survival-horror, similar to Hellnight, and later White Day.
The game follows a bunch of high school students and faculty who are preparing for an upcoming School Festival, when they find they've been locked in overnight. And they soon discover that they aren't alone.
You play as a young boy, Tatsuya Inaba, an exchange student in a Japanese island with strong cultural traditions.
As him and his friends stayed late to finish preparations for a local festival, his schoolmates start dying in strange and inexplicable manners and all the students find themselves locked in. Tatsuya must try to save his friends from the grips of what seems to be ancient entities.
...Iru! is a first person survival-horror game in the vein of Clock Tower, which mean you must hide from monsters in chase sequences to avoid getting killed.
To progress in the game, you will need to talk to other people who are trapped in the school, as well as solve puzzles with the various quest items you can find scattered around the school.