Mogeko Castle is the first game made by Mogeko (site name Deep-Sea Prisoner) in RPG Maker. It was first released in April 1st, 2012 in RPG Maker 2000. A remake made in RPG Maker VX was released in early 2014.
Like Mogeko's third game, Wadanohara and the Great Blue Sea, this is rated by Mogeko themselves as suitable for only those of ages 15+, but this is a Japanese standard of rating and depending on a country's standards, age 18+ might be more appropriate. This game contains very violent imagery, and implied sexual assault. Unlike Wadanohara and the Great Blue Sea, these elements are apparent from the start of the game.
The game starts off with a Mogeko, a cat-like yellow being, who is watching over someone and decides to tell them a story. From there, the game officially begins.
Yonaka Kurai is an ordinary high school student, sitting in a train waiting to get home in order to see her brother, Shinya, who has been gone for some time. As it seems it'll be a long train ride, you are given a choice to go to sleep (you still go to sleep either way), and Yonaka wakes up to arrive in a station called "Mogeko". Confused, she gets off the train and walks forward. Throughout the train station, posters (one says "I WANT GYOZA" written in blood) are posted over the fence, riddled with holes. Yonaka reaches a forest and encounters a group of Mogekos, who say that they'll be "gentle" with her. You have to run until you reach a castle, and must enter unless you want to see a bad ending.
Throughout the course of the game, your goal becomes apparent; you must reach the top floor in order to get back home. In one of the floors, you are thrown into a prison cell while a group of Mogekos decide what to do with you. The prison cell you are thrown into already houses a certain Mogeko who will help you through the game.
The game has multiple bad endings, a normal end, and the true end. This game is meant to be satire on otaku who say things like "my waifu" and the likes, often found posting on certain areas of 2ch.