Katteni Shiyagare — which translates roughly as "do whatever the hell you want" — is a cooperative deduction game for two players consisting of ten double-sided wooden blocks; each block has images of different colors on opposing sides, and overall each of the five colored images appears four times, paired once with each other color.
To set up a game, line up the tiles next to one another and shuffle them without looking at them, turning some of them 180º in order to randomize how the colors are arranged, then turn all ten blocks 90º and arrange them so that each player can see opposite sides of the blocks.
What you're trying to do is create a pyramid with the ten blocks — four blocks on the bottom layer, three on the layer above it, etc. — while following the one rule of construction: You can place a block on top of two blocks only if the color showing on that block matches the color of the one of the blocks below it.
To start play, one player stands a block on end.
The other player then either pushes the block toward you (thereby revealing the other side and burying the side that only you have seen) or pulls the block toward himself (thereby revealing the side you've seen and concealing the color on their side). You then set that block aside to start the bottom layer of the pyramid.
You continue to take turns in this manner, with the other player now standing a block on end and you deciding which way to knock it over and how to place it on the pyramid. After two turns, you might have something that looks like this:
What's your next move? Which block do you stand up, and why? You know that the other side of the green block shows the black guns; does this affect your decision?
What about after two more turns? What now?
If you ever drop a block and that block can't be placed on the pyramid, you lose. Otherwise, you'll complete the pyramid and win.
I've played Katteni Shiyagare four times on a review copy, and I think it's brilliantly minimalist. You can try to track all the information being revealed and which options still exist on the remaining blocks, but either you or your fellow player are in the dark about one side of each tile placed on the pyramid, which means you're left puzzling out why the other player is turning that particular block on its end. Does she think that I see the color that we need to add to the pyramid? Does she want me to pull toward myself because she wants the color she sees revealed? Sometimes you guess or puzzle things out correctly, and sometimes you don't. (Well, I haven't won yet in any of my games, but I can imagine winning sometimes late at night when I'm lying in bed and thinking about games. Sweet victory will someday be mine...)
If you run through how such a pyramid can be constructed, you'll realize that you need to do a few particular things in order to complete the pyramid, but I'll leave those details as an exercise for the reader.
As difficult as Katteni Shiyagare is, you can up the challenge with an expansion pack that adds a sixth color to the game, with the five blocks having that sixth color on one side and the original five colors on the other. Now you need to build a pyramid five levels high — good luck with that!
In addition to the original Katteni Shiyagare game, you can also use the blocks to play a memory game, a game apparently created by Saien on the spur of the moment a few days prior to TGM. To play, throw the tiles onto the table so that one face is hidden. On a turn, flip two tiles over to their reverse sides. If you reveal two tiles that show the same color, remove one of those tiles from play to represent a point for yourself, then take another turn; if the tiles don't match, leave them where they are and let the next player take a turn. Once no more tiles can be claimed (or players repeat a game state since you don't want to set up anyone else), then the game ends and whoever has the most blocks wins.
What else can be played with these blocks? Who's going to think up the next sexy game?