Players create their own Japanese-inspired koi ponds, gradually adding water, shoreline, vegetation, water lilies, koi, lanterns, and other features. Players alternate between acquiring resources and cards and using them to develop their ponds, while pursuing shared and individual scoring objectives. Koi are particularly important: their value increases when surrounded by water and when water lilies are nearby, so players are encouraged to build environments that favour the fish.
Each round is broken into two phases: meditate and work. During meditation, players will select a card from the shared market, which will either provide a one-time bonus, provide a personal scoring condition, or give the player a “helper” – a card that remains next to their board and extends the number of actions they can take during the work phase. When working, players will select any actions they want to perform from their player board and any helpers available to them. Depending on which resources they gathered or stored from previous turns, they can extend their pond, build decorative features, plant water lilies, or introduce new Koi.
The game is relatively simple mechanically, but offers some interesting strategic choices as players have to plan the environment for fish to be introduced into the pond. Nature plays both an aesthetic and mechanical role. Players physically construct the pond through tile placement, with the arrangement of water, plants, animals, and features determining its value. Watching the pond develop is also an important part of the game’s appeal, but its representation of ecology is fairly abstract. A successful pond satisfies spatial patterns and generates victory points. It does not model any negative consequences of human intervention. Players are not required to understand why a particular pond configuration might constitute a healthy ecosystem.
Koi may be suitable for educational hacking, for example, by adding ecological relationships to its existing tile-placement system without fundamentally changing the game. Players could add different plants and animals that provide ecosystem services or depend on one another, with biodiversity replacing or supplementing purely aesthetic scoring. Excessive human intervention could have negative consequences, prompting players to balance the desire to create an attractive pond against maintaining a resilient habitat. The existing goals could likewise be replaced with ecological objectives such as maintaining species diversity or achieving healthy water conditions. In addition, the game can be taught very quickly and plays in less than an hour. The game end is triggered by a deck of cards running out, meaning that the length of gameplay can easily be adjusted.