Janpai Puzzle: Choukou (loosely translated to "Mahjong Tile Puzzle: The Long River", also known simply as Choukou) is a nikakudori-style mahjong solitaire game developed and released by Mitchell for arcades (using Capcom CP System II hardware) in Japan on November 2001.
One of the last games released for the long-running arcade hardware, Choukou is stylized after ancient China (most notably the Three Kingdoms period). By default, the game is configured for the eroge "Gal Mode", which has players undressing four anime-style women, each in traditional attire and each loosely based on figures from the Three Kingdoms period, by solving puzzles. Through operator configuration, this can be disabled entirely.
Similar to other nikakudori-style mahjong solitaire games, players must clear all face-up tiles on the unstacked board by matching tiles of the same face, as long as a path of straight lines (horizontal and vertical) can be imagined between them so that no line touches any other tile and the path must form less than three right angles. Some tiles are face-down and can only be revealed if two of its sides have no tiles adjacent to them, while some tiles are barriers that cannot be cleared. It also includes a special pair of tiles used for power-ups.
The game's defining feature is its game board, which includes two sets of tiles that slowly move towards the center of the playfield, one inching leftward and one inching rightward. If either sets of tiles collide with each other (or with stationary tiles found in some layouts), the player is defeated. Both sets are pushed away from the center when matches are made, and the game's special "Hint" power-up (which uses a special Hint Gauge reminiscent of fighting game super meters) pushes them further while tempoararily holding them in place and showing valid matches. Some layouts take advantage of the positions of these tiles, making certain angles only obtainable at certain positions or having a "line" of tiles from off-screen.
Most game modes allow players to pick from a group of layouts for each Stage (giving them an alphabetic distinction, such as "1-A" and "1-B'). For each mode, losing at a Stage and then continuing gives them the option to either retry the same layout or pick from another. For the Normal mode (with Gal Mode configuration), this switches to a new Stage-specific layout.
Both modes have an optional practice Stage, which gives an overview of the basic game mechanics and does not contribute to the player's overall score. Losing at this stage continues the game as normal.
The Beginner mode has a separate set of Stages that is more ideal for beginner players, with less-troublesome layouts. This uses a separate high score table. There are 10 total layouts in this mode.
Without the Gal Mode configuration, the game includes five Stages, with players choosing from two layouts for each of the five Stages. The game's background art uses the character art from the intro.
With the Gal Mode configuration, the game includes three Stages, with players choosing from three layouts for Stage 1, four layouts for Stage 2, and three layouts for Stage 3. The game's background art uses the first stage art for three of the women characters.
In Normal mode, players play through eight Stages with more difficult layouts. There are 34 total layouts in this mode.
Without the Gal Mode configuration, players choose from multiple layouts for each Stage (five layouts for Stage 1, six layouts for Stage 2, five layouts for Stage 3, five for Stage 4, four for Stage 5, four for Stage 6, three for Stage 7, and two for Stage 8). The game's background art is reminiscent of classic Chinese art.
With the Gal Mode configuration, players are given a layout from each Stage-specific group at random. When choosing a new layout after a continue, it switches to a new random Stage-specific layout. At the first, third, fifth, and seventh rounds, players choose from one of four characters (each of which are shown as the background art and in cutscenes):