Tenshō-Jingo

Kai province (甲斐国, Kai-no-kuni) was the province of the Takeda and home of Ueda Castle. After the Takeda's demise, the place became a very contentious area until Masayuki Sanada was able to claim the area for himself, after allying and double crossing many clans before surrendering to the Toyotomi to prevent any more threats.

Role in games
In Samurai Warriors 3, the H​ōjō attempt to fight off a Sanada-Tokugawa coalition in Lady Kai's second stage. She starts off by repelling the Sanada forces rather easily, before being forced to deal with the defection of Yoshimasa Kiso. Then the Tokugawa take a large offensive to Ujiyasu causing Kai to have to defend her lord and open the Tokugawa encampment from it's exposed behind. Despite the Hōjō's success here however, the vacuum left in the wake of the struggles still allows the Sanada to seize power.

In Samurai Warriors 4-II, the Tenshō-Jingo Conflict is a new map and represents the struggles of Kai province. In Naomasa's story, the Tokugawa and Uesugi ally to fight the Sanada and Hōjō. Naomasa breaks through the Tsutsujigasaki manor and fights off the Hōjō support, isolating the Sanada in the corners. The Tokugawa seize the keep but it's rendered worthless after all the damage incurred by the battle. The Uesugi also get their perspective shown but the outcome remains the same.

In Samurai Warriors: Spirit of Sanada, offers a more in depth look to Masayuki's machinations during chapter 6 and 7. In this time, the Sanada ally and betray the Tokugawa, Uesugi and Hōjō throughout several battles while seizing Numata Castle for themselves. Once Masayuki establishes his own land, he shrewdly surrenders to the Toyotomi. The outcome of these chaotic events inspires him to splinter his clan with Yukimura remaining loyal while Nobuyuki is sent to the Tokugawa when Sekigahara comes so his lineage can survive no who wins.

In Nobunaga's Ambition, Kai Province was designated as an important territory of Shingen and Katsuyori along with Shinano Province.