Some researchers believe his reported magical arts were illusion as a type of group hypnosis.

According to historical documents,  Uesugi Kenshin had heard of Danzō's reputation, which had led for him to invite Danzō to his prime castle. Kenshin decided to test Danzō's abilities by challenging him to sneak into a certain castle and to retrieve a prized naginata  from one of his retainers, Naoe Kanetsugu.

Danzō infiltrated Kanetsugu's heavily guarded castle and not only succeeding in stealing the naginata, but also captured a young servant girl.

Kenshin then realized that Danzō would be a very useful ally and took him into his service. However, Kanetsugu plotted to kill Danzō (according to another version it was Kenshin himself who ordered his death, perceiving him to be too skillful and thus dangerous), forcing him to try to defect to Takeda Shingen, Kenshin's rival.

Suspecting Danzō to be a double agent, Shingen however ordered him to be killed.^[4] Danzō was captured by Takeda's men and executed through decapitation.