WARNING: MAJOR SPOILERS ahead for the Shōgun finale.
Ochiba-no-kata’s letter to Lord Toranaga made all the difference in the Shōgun finale. As Toranaga’s master plan for Crimson Sky is finally revealed in the final moments of Shōgun episode 10, John Blackthorne ends up being one of the few people in Toranaga’s company that survives until the end following the shocking death of Mariko in Shōgun episode 9. Ochiba-no-kata also shows her true colors by betraying Lord Ishido despite having a complicated past with Toranaga.
After a long-awaited reunion between Ochiba-no-kata and Mariko in Shōgun episode 9, Mariko starts writing a poem about a leafless branch that would ultimately become her last. Lady Ochiba discusses the poem with her son, the young Heir of the Taiko, whom she has dedicated the rest of her life to protecting. She finishes the poem that Mariko had started with the final profound words that Mariko had spoken to her, which were “Flowers are only flowers because they fall.“
The final twist of Shōgun was the sudden reveal that Ochiba-no-kata and Lord Toranaga had been secretly working together to betray Lord Ishido. Toranaga is seen reading the short poem from Ochiba, which was escorted secretly from Osaka to Ajiro, and is greatly relieved to see that she has agreed not to support Ishido at the upcoming Battle of Sekigahara. Her poem reads, “If I could use words / like scattering flowers and fallen leaves, / what a bonfire my poems would make.“
Toranaga explains that the poem he reads aloud are words from Lady Mariko, indicating that Ochiba-no-kata had sent him one of her poems as a cryptic message. Through Lady Mariko’s poetic words, Ochiba-no-kata confirms that she more or less agrees to betray Lord Ishido in the upcoming war. “Fallen leaves” is a direct indication of Ochiba, whose name translates to “fallen leaves”. The poem essentially says if Ochiba could speak the truth, it could create a “bonfire” that would destroy all.
Lord Toranaga understood that cryptic message hidden within Mariko’s poem from Ochiba-no-kata’s letter. Although the letter doesn’t directly confirm Ochiba’s intention to betray Ishido, Toranaga is reassured that the Heir’s army won’t fight for Lord Ishido through the meaning of the poem and the implication of using Mariko’s words to send the message. In this way, Mariko truly became the final piece of Toranaga’s elaborate puzzle to rise to power in Shōgun.