The “Plum Tree” Plan

The “Plum Tree” Plan was a concealed betrayal scheme inside Yabu’s Izu Musket Regiment: if Yabu switched sides during battle, fifty-four men knew of a plan to assassinate Toranaga, Naga, and Lord Sudara. Its disclosure reveals the danger embedded within Toranaga’s own military ranks, but the response is as consequential as the conspiracy itself. Toranaga checked the report, used the ship’s burning as an opportunity to remove the plotters, and treated the informant’s loyalty as valuable without mistaking it for grounds for complete trust.

Origins and Political Context

The plan took shape against an unsettled question of allegiance. When Toranaga offered Yabu rule over Izu, Suruga, and Totomi if he won the war, Yabu welcomed the prospect but refused to become Toranaga’s vassal. He would accept Toranaga as ally and leader and commit his life and possessions to Toranaga’s side, yet insisted that Izu was his hereditary domain. He invoked his oath to his father and the Taikō’s confirmation of the fief for his successors, saying he had sworn not to accept another liege lord before the heir came of age.

That distinction between alliance and fealty gives the conspiracy its particular tension. The plan was not described as an attack already underway: its condition was Yabu’s possible, sudden change of sides during battle. The officer who exposed it said that this contingency would make Toranaga the primary target, followed by Naga and then Lord Sudara. Yabu’s resistance to formal vassalage does not, by itself, establish that he intended to betray Toranaga; the disclosed scheme instead shows how his officers prepared for that possibility, and how precarious a military alliance could be when its obligations remained contested.

Omi’s Discovery and the Report

Kasigi Omi had proved central to Toranaga’s assessment of Yabu’s household. Toranaga had originally bought Kiku’s contract to keep her from Omi, whose attachment to her was one of his weaknesses, and held the contract as a prize to give or withhold until Omi had demonstrated his allegiance and helped remove Yabu. Omi did so. He suggested investigating the servants, and many of Yabu’s ideas had, in fact, originated with him. A month before the later disclosure, Omi had uncovered the secret plot involving Yabu and officers in the Musket Regiment.

When Omi reported it privately at Mishima, he identified Kiwami Matano of the Third Izu Regiment as being outside. Matano, a middle-aged officer, then laid out the scheme, supplied its passwords, and explained how it would work. He described the plan as conditional: it was intended for use if Yabu decided to change sides during the battle. The targets were to be Toranaga first, then Naga, then Lord Sudara. The report thus supplied both the intended victims and the circumstances in which the conspirators expected to act.

Verification and Removal

Toranaga asked when the plan had been ordered, how widely it was known, and who had authorized it. Matano said that it had been organized shortly after the regiment was formed and that fifty-four men knew of it. Omi had received all their names in writing. Matano further reported that Yabu had personally confirmed the plan, code-named “Plum Tree,” before his most recent departure for Osaka. These particulars made the disclosure actionable: it was not simply suspicion about Yabu’s loyalties, but an account with names, passwords, a chain of knowledge, and an alleged confirmation by Yabu himself.

Even so, Toranaga initially considered whether Omi and Mizuno might have invented the plot to discredit Yabu. He sent his own spies to establish whether the report was true rather than accepting it at face value. Their investigation confirmed it. The burning of the ship then provided a cover for removing the fifty-three conspirators, all of whom had been placed among the Izu guards on that night. The account establishes their removal, but does not specify their individual fates; the operational consequence it emphasizes is that the men implicated in the scheme were taken out of the guard force.

The Informant and the Meaning of Loyalty

Matano asked permission to commit seppuku, presenting his long concealment of the information as shameful. Toranaga instead commended his loyalty and promised him a fief worth five thousand koku, on the condition that he keep the matter secret until instructed otherwise. After the plot was verified, Matano was sent to the far north with a good but modest fief. His reward acknowledged the value of his disclosure, while the difference between the promised five thousand koku and the fief ultimately described marks the limits of that reward.

Toranaga did not convert Matano’s service into unquestioned confidence. He later agreed with Sudara that Matano was the most dangerous of the informants, and said that he would be watched throughout his life and never trusted. His response distinguishes the usefulness of an action from certainty about the person who performed it: Matano had helped expose an authentic conspiracy, but had kept its knowledge for a long time. Toranaga’s stated principle was to recognize good in bad people and bad in good ones, preserve what was good, and remove what was dangerous rather than discard people wholesale. The episode therefore makes the “Plum Tree” Plan not only a military threat but a test of political judgment: Toranaga must uncover betrayal, dismantle its network, and still decide how much trust any survivor deserves.