Kai-oi: Rules and How to Play
Kai-oi — Shell Matching is a traditional game for 1–6 players, about 10 minutes. Find the ground shell matching the drawn shell and collect the most pairs.
Setup
- Each real clam supplies two matching halves: a ground shell and a drawn shell.
- Use 26 pairs, or choose a short 12-pair game. Both orders are shuffled each game.
How to play
- Choose a ground shell to mark its original place with a hand. Everyone, including watchers, sees the same hand. Change your choice before Check.
- Press Check to move it beside the drawn shell. Wait 3 seconds after they line up for a circle and Match, or a cross and No match. A match earns a pair and another turn; a miss passes the turn with the same drawn shell.
- Collected places stay empty. The default limit is 20 seconds, shown by a shrinking ring and a number. At the deadline, a selected shell goes to Check; no choice costs one try and passes the turn.
Winning and scoring
- When no drawn shells remain, most pairs wins. All players tied for first win; an all-player tie is a draw.
- Solo play counts presses of Check, including timeouts. Aim for fewer tries. Your personal best is stored on this device.
- The shells in this game are photos of clams bought at AEON Higashikurume.
Defaults on this site
| Item | Default on this site |
|---|---|
| Players | 1–6 players (set automatically by the party size) |
| Turn time limit | None by default (the host can set 30 or 60 seconds) |
| If someone drops mid-game | Reopening on the same device returns you to your seat. If you do not return, the CPU plays in your place. |
| Draws | In ranked play, a draw counts as halfway between a win and a loss for your rating. |
| Source of the rules | Based on the standard reference rules |
Rules supervised by Qdan, Inc. (based on the standard reference rules)
House rules
Defaults follow the standard reference rules. The party can change these.
| Name | Description | Default | Changeable |
|---|---|---|---|
| Pairs | Choose 12 pairs for a shorter game. | 26 pairs | Yes |
| Time limit | At the limit, check the selected shell; without a choice, pass the turn. | 20 seconds | Yes |
Terms
- Ground shell
- The left half, placed in the ring.
- Drawn shell
- The right half, drawn into the center.
- Shell tip
- The pointed top of the shell. Nearby patterns help you compare.
FAQ
Is this Kai-awase?
Kai-awase is also used as a name for this shell matching game. Here you compare the natural outer patterns, rather than interior paintings or poems.
Are misses recorded?
The cross stays until the next action. Miss history is not shown. Collected pairs can be reviewed from the menu.
Can I change the time limit?
After starting the party, choose no limit, 10, 20, 30, or 60 seconds in setup.
Play now with these rules
Last updated 2026-11-11 · Run by Qdan, Inc.