There are various theories regarding Nobutora's banishment including the theory it was due to `inappropriate behavior' such as Nobutora's military services in invasions outside the country or increasing taxes during poor harvests, which are described in Kai Province historic materials such as "Katsuyamakia" (the chronology of Kai Province) and Kogaku-ji Temple, the theory that Nobutora's banishment was a retirement based on agreement, which was described in "Kai koku shi" (Records of Kai Province), and another theory is that Harunobu conspired with Yoshimoto IMAGAWA.
この信虎追放には『勝山記』や向嶽寺など甲斐国内史料に記される信虎の対外侵攻の軍役や凶作に際しての重税など「悪行」を原因とする説から、『甲斐国志』による合意による隠居であったとする説、今川義元との共謀説などの諸説ある。