When Anna Sawai first read the script for the ninth episode of Shōgun, “Crimson Sky,” she didn’t feel especially emotional. “I already knew the story, so it was more like, ‘Okay, how are we going to shoot this?’” she recalls. “I was just distancing myself and thinking about the technical stuff. That’s how I had to do it, because otherwise I would have to carry those emotions for way too long.”

Indeed, for the actor behind Shōgun’s tragic hero, Lady Mariko, everything came to a head only when cameras started rolling. Even more than a year after wrapping the series, the emotions didn’t fall away: “I’d remember how I felt playing certain scenes, and I would just cry.”

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Mariko dies at the end of “Crimson Sky” in an act of ultimate sacrifice. She puts herself on the front lines in Osaka, as part of her Lord Toranaga’s grand plan to seize power and expose the deception of his rival, Ishido (Takehiro Hira). The previous episode ended with Mariko surprising Toranaga’s men, including the captured English sailor (and her love interest) John Blackthorne (Cosmo Jarvis) and the wishy-washy Yabushige (Tadanobu Asano), by joining them on their voyage to Osaka. This week’s installment carefully, slowly reveals the true nature of her participation, beginning with a flashback to her traumatic family history and culminating in a double-cross by Yabushige that leaves Mariko with nowhere to turn.

Yet Mariko is at peace with her fate. Shōgun has explored the ripple effects of her principled father’s (and, in turn, her family’s) unjust death, and her desire to join him in the next life by committing seppuku (an honorable form of taking one’s own life). Toranaga (Hiroyuki Sanada) knows this desire, and has offered her an exit plan that will serve him at the most pivotal moment in his fight. Mariko would go to Osaka, ostensibly in mourning for Toranaga’s slain son, and reveal the brutal tyranny of Ishido’s regime to her community in the process. This would change the course of the war between the two men, and thereby the course of Japan itself—exactly what happened in the case of Hosokawa Gracia, the real-life inspiration for Mariko.

“It was a lot of mixed feelings for me because, in a way, that’s what she wants,” Sawai says of Mariko’s fate. “She wants to serve her lord. She wants to fulfill her role. She’s happy to do it. She doesn’t want to just have an easy life.”

Mariko’s first big scene in “Crimson Sky” arrives when she tries to leave Osaka, with her own army surrounding her. She knows Ishido and his men will not let her go, but because, theoretically, she has been ordered to leave at Toranaga’s request, she goes forward anyway, as Ishido’s guards attempt to stop her at every turn. Eventually, the guards fight back, and Mariko’s men begin to fall in bloody succession. Her own samurai training—which women of the era typically were forbidden from acting upon—at last comes into play in a thrilling, harrowing fight scene.

“Just experiencing that was so heartbreaking to me. I was not myself, I’m just Mariko at this point,” Sawai says. “We had a short scene that we shot after this fight, where Mariko goes and cries in the corner, and that’s exactly how I was feeling. I had to be powerful in the moment, but you see all these people sacrificing their lives and dying in front of you.”

Mariko survives, but announces that she will commit seppuku for her transgressions, even as Ishido faces mounting pressure to permit Mariko to leave as her lord instructs. In an agonizing sequence, we watch Mariko prepare to end her own life, with no one stepping up to second (or support, as the ritual dictates) the act. Her son is in attendance. So is Blackthorne, the man who has become her close friend and lover. Eventually, he steps up—a symbol of his enduring affection for her, and an indication that after a full season of not understanding her attraction to death, he sees and respects what she values. The camera holds on Mariko as she slowly inches the sword toward her stomach, with Blackthorne behind her, until Ishido stops the proceedings at the last possible moment—departure permits in hand. Mariko and Blackthorne gasp in shock. The audience does too.

For Sawai, again, the experience of playing all that hit hard. “When I read the scene, it was just like, ‘Okay, this is very dramatic.’ But then I remember seeing the son in the corner, and it was like, I can’t believe I’m showing this to him,” Sawai says. “Mariko had to see her whole family die, and now she’s doing the same thing to her son. It was a big sense of guilt and it just surprised me. It was nothing that I had expected.”

That raw, instinctual anguish is all over Sawai’s performance, in which the near-seppuku marks a searing kind of climax for the character. From there, she sleeps with Blackthorne one last time before their temporary residence is raided in the middle of the night—a dark, murky, terrifying attack that, after some panicked confusion, ends in her death. Ishido could not actually let her leave, and so with an assist from Yabushige, he has facilitated her demise in secret. She dies holding back a door as it explodes, saving others who are in the room with her—the sacrifice she was dedicated to making for so long.

“You have nothing to prove to these people. You’ve made your point. There’s no need to die for it,” Blackthorne says to Mariko at one point in the episode. Her reply says it all: “There is every need.”