Kikko

A hexagon board. One, two or three dots in each cell. Every line that carries an arrow must add up to the number on that arrow. When every arrow turns green, the board is solved.

That is the whole rule. The rest is bigger boards and the constraints that land on top of them.

— PLAY —

• 15 chapters, over 2000 generated boards • No timer, no lives, no streak. Think as long as you like • One tap to undo, one tap to clear • A hint when you are stuck: it opens one cell's true value

— NEW CONSTRAINTS —

Later chapters add rules, and each one is taught on its own, on a calm board:

• Region sums — cells wrapped in a mizuhiki cord share a total • Seals and bonds — cells tied to each other

— LOOK —

Washi paper and sumi ink. Each chapter has its own season colour. Night has its own paper: sumizome, not a darkened day but a separate world mixed from indigo.

The stones are go stones. Other stone sets are available in the market.

— QUIET —

The sound palette is koto plucks on the hirajoshi pentatonic, struck bells and dry wooden knocks. Nothing has a sharp attack. Playing it muted is part of the design too.

— NO INTERNET NEEDED —

Every board is on the device. Works on a plane, on the metro, out of coverage.

— SUPPORTER —

A one-time purchase: removes every ad and gives a purse of coins. Not a subscription, it does not repeat.