Among his students were the daimyōs Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu, the three great "unifiers" of feudal Japan.

In 1582, Nikkai, at the behest of Nobunaga, was involved in a notorious game at the Honnōji Temple against his rival, another Nichiren priest, Kashio Rigen (鹿塩 利玄 b.

The game is traditionally held to have taken place on the eve of the treacherous Incident at Honnōji, (in which Nobunaga was forced to commit seppuku), and is said to have ended in a "triple ko".

The triple ko may have occurred, somewhat implausibly, in unrecorded remaining plays, or in another game that day, but in the end, there is no evidence that this is more than a good story.

In 1587, Nobunaga's successor, the regent (kampaku) Hideyoshi gave Nikkai an official position, (forerunner to the office of Go-dokoro), granting his temple an annual four koku of rice and setting up a tournament that he attended in person.

This system persisted over two and a half centuries, until the collapse of the Tokugawa government itself in the Meiji Restoration.

The beginning of the oshirogo matches in Edo, seat of the Tokugawa government, meant that at the end of each year, Sansa had to travel east for a month.