This theory is based on the fact that the heads of Sakon and Yoshitsugu OTANI, taisho of the 'western' army who died in the Battle of Sekigahara, were never found (in the case of Yoshitsugu OTANI, his close adviser, Gosuke YUASA, assisted him in committing Seppuku [suicide by disembowelment] by beheading him and later died without telling anyone where the head was buried, and it was therefore never found), and there were many people who said that they saw Sakon in Kyoto after the battle, but the truth is unknown.
この説は、関ヶ原の合戦で戦死した西軍大将として大谷吉継と共に首が見つかっておらず（大谷吉継の場合は側近の湯浅五助が切腹の介錯を行い、首級を埋めた場所を語らず死亡したため発見されなかった）、さらには合戦後に京都で左近を目撃したと称する者が相次いだためとされているが、真相は不明。