Yoru no Senshi: Shingen no Shinobi

Maruko Sasanosuke, a Kouga ninja who had infiltrated Takeda Shingen's residence, as a vassal, was hiding in plain sight, waiting for an opportunity to assassinate Shingen with Magobei, another infiltrated ninja master. However, an encounter with Shingen's second daughter, Hisahito, changes Sasanosuke's fate forever...
This is the story of a young ninja who tries his best to survive in the turbulent world of Shingen's rival, Uesugi Kenshin.

(Source: Leed, translated)