Through their publishing of puzzle games over recent years, Nikoli have helped popularize common puzzle types such as Sudoku and Kakuro around the world. However these two particular puzzles were originally developed in America.
While appearing in many games, Nikoli puzzles have most extensively appeared in conjunction with Hudson Soft on the DS through their 'Puzzle Series' games, and other titles such as Illustlogic. However, these have not been published outside of Japan.
Nikoli have also been responsible for developing several kinds of original puzzles which have appeared in game form, and believe the worldwide success of their puzzles is largely due to their language independence, featuring universal concepts and only numbers, not letters.
Some notable example of Nikoli's own puzzle types:
Probably the most recognised of Nikoli's puzzles, Slitherlink requires the player to draw a path onto a grid filled with various 'number clues'. Numbers indicate the number of sides of that square which form part of the path.
The finished pathway has to form a single closed loop. Consequently, the logic of the game involves avoiding a path that splits, reaches a dead end, or forms two or more loops.
Also known in the west as Light Up, Akari is one of the simpler puzzle types. Akari starts with a Crossword style grid with several squares blocked out. The aim of the game is to place 'lights' around the grid, which illuminate squares in that row or column, unless blocked by a filled square.
Numbers on some squares indicate how many lights should be in the adjacent four squares. A correctly solved puzzle should have all squares lit, and no two lights should illuminate each other.
Like Sudoku, Hitori is about a square grid full of numbers. However, Hitori is almost the opposite of Sudoku, as it starts with a full grid, and numbers must be removed. The aim of the puzzle is to block out squares, so that no row or column contains more than one of any number.
The other conditon of the game is that all remaining numbers should connect to each other (not counting diagonally). Tradtionally, numbers are circled when they are confirmed as required.
Conceptually one of Nikoli's more complicated puzzles, Nurikabe is named after a 'wall demon' from Japanese folklore. Playable on a grid of any size, the aim is to use the initial number clues to construct a wall pattern which partitions the remaining squares into groups.
The size of each group must equal the number on a square within it. The player must therefore avoid groups which have no number, or more than one number. Similar to Hitori, the 'wall' must exist as one continuous structure, and additionally not contain any 2x2 squares.
Other puzzle types featuring in Nikoli publications include Numberlink, Fillomino, Ripple Effect and Hashiwokakero.
Nikoli is named after a race horse.