1. Introduction
Koi-koi here refers to the classic Japanese Hanafuda card game.
Here I just assume you already know how to identify the cards and the basic yakus. However I would still make a list of them to make sure the version of the game you player is at least similar to the one discussed here. The translation might be a bit off and the values could be different, but I believe the general rule would still apply.
| Name | Value |
|---|---|
| Goko | 15 |
| Shiko | 10 |
| Ameshiko | 8 |
| Sanko | 6 |
| Inoshikacho | 5 |
| Akatan/Aotan | 5 |
| Tsukimisake/Hanamisake | 3 |
| Tan/Tane/Kasu | 1 |
2. Begin the match
It is definitely advantageous to become oya. However, since the oya of first round it is determined by randomized process, there is really much thing to be discussed here.
After get the hand, you should get an idea of which yaku your hand can possibly make, taking the cards on table that you can definitely get at the first round into accounts. If you have three of the Hikari exclude the Ono then just aim for Sanko or higher; if it is Tane or Tan, then see if you can make it to Inoshikacho/Akatan/Aotan, or stay focus on get five of a kind as quick as possible. If it is Kasu, well, good luck then.
2.1. How to determine if a card can be acquired
If it is one of the following conditions, it is safe to assume you can get the card later, and is it better to do so for different reasons. Otherwise you need to be fast.
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There are one in the hand and other three of the same month on the table: congratulation! You can just pick up them all at once, it is better off pick other valuable cards from different months first, since your opponent won't able to pickup the three anyway.
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There are two of the same month on the hand and two other card on the table: they are all yours, but it just took some rounds to get them, if you can pick up any other cards, pickup them first to slow done your opponent.
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There are two of the same month on the table and one other card needed is in the hand: it is still safe to get the card later. Just pay some attention if the opponent is going to make a Tan/Tane/Kasu yaku soon.
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There are two of the same month on the hand, one of them is needed, and one other card is on the table: you may pick up the one in your hand a few rounds later, but just don't be too late.
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You have a pair of the same month, the other pair is not on the table nor already acquired: you need to be patient for a while to prevent the situation that your opponent has one or more cards of the same month in the hand.
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You have one of the left pair of the month, the other pair has already been acquired: you can only wait in such situation, isn't it?
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There is one card needed in the hand, no other cards of the same month are on the table: you need to wait patiently for them to show up if you don't want to lose the valuable card.
3. Mid-game strategies
The main mid-game strategy is as simple as grab any valuable cards and prevent your opponent form any yaku, while making your yaku as fast as possible.
Postpone taking the cards that will 100% be in your pocket and reduce the card your opponent can take as much as possible as an attack if you don't you can form a yaku right now.
3.1. Determine the value of the card
There are a few cards that worth extra attention.
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Moon, Curtain and Sake: they can easily form the Tsukimisake and Hanamisake yaku, and even more powerful if combined with Sanko. Even when you cannot the related yakus your should still make some effort preventing the opponent to form the yaku. However, if is has become to the situation that neither of the player can form the yaku, it is pointless to collect them.
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Other Hikaris are not worthy if compared to cards that belonging to the yaku your are current pursuing, especially if it is part of Aotan or Akatan. Always remember that you still need a yaku to win.
4. Defense strategy
Although this is not an official player terminology, I would take defense in this game as the strategy to play in a round when there are no cards you can take on the table.
It is now a good time to get the pairs that are in the hand, remember put down the less valuable card first since it is possible for the opponent to have card of matching month in the hand.
At this time, you should really consider pursuing Kasu by taking away the cards on the table as much as possible.
5. When to call Koi-koi?
The rule is, you don't. Unless you can 100% be sure that you can make another yaku in next couple rounds plus it is impossible for the opponent to make any yaku before that. Even it is when you made a Tsukimisake/Hanamisake at the very first round, you should still go to next round as the oya with what you have to keep the advantage you've got.