Fill a room of tatami mats with numbers: every mat holds 1 to its length once, every row and column holds each number twice, and equal numbers never touch. Every board is unique and solvable by logic — beat each level's shrinking clock.
Tap a square to select it, then tap a number on the pad below to write it; ⌫ clears the square. Tapping the selected square again steps it through the numbers and back to blank, which is the quickest way to enter values. Fill the whole room before the bar above the board runs out.
The room is tiled with straight mats, each outlined by a dark cloth edge along its long sides. On levels 1 to 4 the room is 6 × 6 and every mat is 3 squares long, so it holds the numbers 1, 2 and 3 once each. From level 5 the room is 8 × 8, the mats are 4 squares long and hold 1, 2, 3 and 4. A finished room also obeys two more rules: every row and every column contains each number exactly twice, and two equal numbers may never sit side by side — not even across the border between two mats.
Numbers on round seals are given and cannot be changed. A number turns red when it breaks a rule — it touches an equal number, its mat already has that number, or its row or column has it more than twice — and the line under the board says which rule. Selecting a square lightly highlights its mat, row and column so you can check them at a glance.
Level 1 gives you 200 seconds and every level after it has 5 seconds less, with no minimum, so level 40 has only 5 seconds and no game can go past it. The first few levels show a few extra numbers to help you in. The clock only runs while a board is on screen and keeps running if you switch apps. When time runs out the solution is shown and the game ends. Your score is the number of levels you cleared; equal level counts are ranked by total solving time, to a tenth of a second. Every board is generated fresh, has exactly one solution and can be solved by deduction alone.
Start with the mats, because they are the most crowded rule. A short mat of 3 that already shows two numbers is finished for free — the last square takes the missing one. Even one given number helps: in a mat of 3 holding a 2, the other two squares are 1 and 3 in some order, and the 2 also forbids a 2 in every square that touches it, inside the mat or out.
Then count along the lines. Each row and column needs every number exactly twice, so the moment a row shows two 3s, every other square in that row loses 3 as a choice. Turn it around too: if only two squares in a column can still hold a 1, both of them are 1s. A mat lying along a row supplies that row with one of each number, so a row made of two such mats is already balanced and its remaining work is only about the touching rule.
The touching rule hides the most useful trick. Two equal numbers in a line can never be neighbours, so if the squares that can still take a 4 in some row form a run of three in a row, at most two 4s fit there — in the outer two squares. Whenever those runs can only just hold the copies the line still needs, the positions are forced: a run of three takes its ends, a single square takes the number outright. Many boards that look stuck give way to exactly this count.
On the clock, keep a rhythm rather than rushing. Sweep for finished mats and full lines first, write everything that is forced, and only then look for the spacing trick. Tapping the selected square again is quicker than the pad once you know the answer. Levels shrink by 5 seconds each, so the 8 × 8 rooms that take you three minutes at level 5 have to fall in about a minute by level 29.