DoorDoor is a puzzle game that was created by Koichi Nakamura, the man who would go on to create the venerable Japanese RPG company and Mysterious Dungeon developer Chunsoft. Published by Enix, DoorDoor was the company's very first foray into the video game marketplace, having been created as the result of a contest it held in Japan to find its first worthy product to release. Putting players in the role of baseball cap-wearing Chun, the gameplay involves Chun trapping monsters behind doors, with different level layouts and monsters necessitating a variety of strategies to win.
DoorDoor's gameplay entails luring monsters into open doors that can then be shut, permanently trapping them for the remainder of the level and boosting the player's score. Since the monsters otherwise stalk Chun in a manner similar to Pac-Man's eternally pursuing ghosts, much of the gameplay revolves around taking advantage of their path-finding programming and other unique characteristics in order to defeat them. Some creatures have more overt special abilities such as the ability to jump with the same timing as Chun, while others are more subtle, possessing things as simple as slightly faster running speeds.
DoorDoor's major source of puzzle solving in addition to the monsters and their routines lies in the doors themselves. Given that most of the doors only open and close in one way, the monsters must first be brought to the door from a specific direction. Only once they enter it can the door then be fully closed by having Chun walk over it from the opposite direction. While multiple monsters can be trapped behind one door, doing so can be a gamble; monsters that are inside a door that is still open will only stay in there for a few seconds. If the player is too slow to close the door, the monster will reenter the level, possibly killing Chun in the process if he happens to be nearby. Doors that have also been used to previously trap a monster cannot be opened once they have something inside.
Dying, however, does not result in the respawning of all monsters, as only the monsters that were still free will remain when the level restarts. Likewise, the doors that were used to trap monsters can be used once again to capture the remaining ones. In scenarios where the player still has monsters roaming but no usable doors remaining, this is a mechanic that sometimes has to be exploited, something that was deliberately designed into the game and its level layouts.
The release of DoorDoor came about as the result of Enix needing a game to publish as its first push into the Japanese video game marketplace. Given that the company was not originally intended to have video games designed and released by internal teams, it was necessary to recruit outside talent. In order to accomplish this objective. Enix decided to hold a national contest for programmers. Out of that contest came the hiring of Koichi Nakamarua, a high schooler at the time, who came in first place with DoorDoor as his entry. After Enix acquired the rights to the game, it became a major hit, selling over 200,000 copies. This process of finding outside help to create and sell games instead of always doing it within the company helped lay the groundwork and standards to come in future developer-publishing relationships throughout the video game industry.