According to "Koyo Gunkan" (a record of the military exploits of the Takeda family), he left a will, `my death should be kept secret for three years, and my dead body shall be sunk into Lake Suwa' and also left his last word, `serve as koken (guardian) until Nobukatsu succeeded the position, and relyed on Kenshin UESUGI in Echigo Province,' to Katsuyori.
『甲陽軍鑑』によれば、信玄は遺言で「自身の死を3年の間は秘匿し、遺骸を諏訪湖に沈める事」や、勝頼に対しては「信勝継承までの後見として務め、越後の上杉謙信を頼る事」を言い残した。