The island is also known as Ninpou and though there are numerous settlements they are all considered part of the same city.
Ninpou is perhaps the largest land-mass on the planet and dominated primarily by large mountains. The city stays along the coast and completely rings the island. The entire coastline is dotted with natural and artificial harbors. Goods and people move about mostly by water. Okaeshi Harbor is one of the principal ports.
A few large rivers allow ships to sail dozens of miles inland, extending the reach of the city along those rivers. However, the interior of the island is sparsely populated.
The highest mountains are along the outer-rim between the city and the interior. The interior is mostly forested and provides a steady supply of timber for ships. Most Ninja vessels are built at Ninpou.
The bulk of the interior is dominated by the massive lava dome of an extinct volcano. Rainwater drains off this and collects into rivers which flow through mountain canyons into the sea. A few large lakes accessible either directly or by locks also see a great deal of habitation along their coastlines; however, these regions are mostly part of the timber trade, with most ninjas preferring to live near the ocean.
The Ninjas have an Emperor; but they also have a High Council, who run the empire day-to-day while the Emperor makes the most-important decisions. Occasionally someone thinks that either Emperor, or High Council, could act alone; but this idea has not been put successfully into practice, before the time of the story.
Since much of Ninpou is on mountain slopes, flat areas are highly prized. The flat regions tend to be the wealthiest and most affluent, with the poorer parts of the city dug-in along the slopes.
Above the city the mountainsides are heavily terraced to provide agricultural space. Flat land is far too valuable. Windmills are used at various stages to pump water through natural basins into higher steps. Though the labor is fairly intensive, the crop yields are very high. The rice terraces of Ninpou are so productive that most of the rice consumed throughout the Ninja empire is grown there.