
Unlike the sequels that follows you take on the role of Kenta, a high school student trapped by Isaku, the eldest brother of the Itou Family on the last floor of an abandoned school building together with fellow classmates and a teacher. The main objective of the game is to have the player and his companions escape from a locked school building, and to avoid having your companions captured by Isaku. The only way out is through a stairwell, the doors of which are locked on every floor. The player must search the rooms on each floor for clues and items that will lead him to locate the keys that will open the stairwell doors and allow him to descend to the next level and ultimately to a final confrontation with Isaku himself.
Isaku is a Japanese visual novel of 402,379 characters, with 9,165 unique words and 1,701 different kanji. Its difficulty rating on Jiten is hard, 3.0 out of 5. The full vocabulary list ranks all 9,165 words by how often they appear, and you can study them on Jiten or download them as an Anki deck.
Here are some of the words that appear most often in this media, as well as a sample of its rarer vocabulary.