Cosmo Jarvis has had some trouble shaking John Blackthorne off. The British actor developed a true kinship with his Shōgun character over an extensive 11-month-long shoot, almost as if he were experiencing the FX limited series’ epic, dangerous adventures himself. When all was said and done, and it was time to go home, Jarvis felt “kind of sad,” as he softly puts it in our wide-ranging conversation about the finale and overall series (all of which is now streaming on Hulu). His melancholy tone suggests that feeling hasn’t quite faded yet, more than a year later.

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Adapted from the 1975 James Clavell novel, Shōgun delivered an immersive, deeply moving saga for viewers too. The show begins with Jarvis’s Blackthorne, a headstrong English sailor traveling to Japan circa 1600, left shipwrecked and fighting for survival. Hoping to disrupt the country’s exclusive trade agreement with the Portuguese, he is instead pulled in unexpected directions by the brilliant and cunning Yoshii Toranaga (Hiroyuki Sanada), one of a handful of lords angling for control in a massive power vacuum, who takes Blackthorne in as an asset in his vague, grand plan for the future of Japan. Over the course of the series, Blackthorne travels the country with Toranaga and his army, part captive and part samurai in training. Along the way, he falls hard for his translator, the Catholic convert Toda Mariko (Anna Sawai), and comes to understand the nuances and complexities of Japanese culture in his mission to simply stay alive.

Best known for his smaller roles in Peaky Blinders and Persuasion, Jarvis charts that evolution brilliantly, introducing Blackthorne with a near feral energy before slowing him down, taking in the brave new world around him. The finale finds Blackthorne on particularly uncertain ground, with Mariko having sacrificed her life in service of Toranaga’s plan—but not before secretly negotiating to save Blackthorne’s life, exchanging his ship and weaponry with the Portuguese for his protection. With the constant threat of imminent danger finally receding, he’s left in a sort of purgatory, to consider his future an ocean away from his home that he may never see again.

The finale opens on a disturbing vision of the future, with Jarvis in elaborate old-age makeup as Blackthorne regretfully contemplates a life of ravaging the Japanese land, as his initial plan had dictated. The scene takes on a hue that is more nightmarish fear than literal flash-forward, though: The series ends on Blackthorne aligned, if a bit uneasily, with the man who captured him back when this series began. Blackthorne’s story in Shōgun has been one of letting go of his cold-hearted mission, of embracing a place he expected to use for his own gain. It’s that complex inner conflict that you sense Jarvis will miss the most.

Vanity Fair: What do you remember about wrapping this final episode? What was it like moving on, or what did you do once you had finished?

Cosmo Jarvis: It was a really long shoot. It's very difficult to explain. Blackthorne totally preoccupied and consumed me, and had for so long. When it came to the final shot, it was just horrific, because it's only then that I suppose Blackthorne had to be left behind and all of these adventures had to be left behind. And it was just kind of sad, you know? I suppose in a way it was relieving, but also, then you're just another unemployed actor, and you don't know what's going to come next. I don't know what I did afterwards. I think I just came home to England. I just came home and couldn't believe what just happened.

I feel like for a lot of actors in your position, it would be a relief to come down from that. But it sounds like you were loving that total immersion.

Yeah. John has so many admirable traits, so many traits that I envy and that I respect. And after being that way for so long, it really gives you an indication as to, I guess, what it would be like—what it's like to be him. Being someone like that for that long, I preferred him to myself in a lot of ways, and everything that came with him—not just fictionally, with regards to his predicaments and adventures and growth as a man, but also in terms of his general sureness, his confidence in himself, and his ability to adapt to any situation, even if he's not entirely sure that it's going to pan out. He’ll just commit to it. There are so many amazing traits that he has, and it was 11 months. In some ways it's a relief, because the job's done, and we can only hope that it's been done well, and we can only hope that we've done right by all of the other thousands of people that worked on the thing. But at the same time, it's really sad to leave that guy behind.

I can understand that, and you'd stayed in character pretty much as much as you could, right, over the course of the shoot?

I mean, I guess? I don't know what that means.

You tell me.

The actor still has to know that they have to come to work, and they have to get in a car, and they have to do their job. But I maintain as many of the things that, to me, comprise a person's character that I can for as long as I can, because I guess that's what my job is. I don’t know. Maybe I'm just superstitious.

How much did you know about Blackthorne's arc going into the show? Did you read the book beforehand, or get an outline from the writers?

I had no idea where he would be ending. I knew the vague set-up: I knew the situation, I knew the character, I knew where he was from, and what his purpose was. But in terms of any foresight that was available from the book, as to where he would end up in this adaptation or how he would end up there, I didn't. All I would do is use the book as a document that I could refer to, only up until the point where it became relevant to whichever portion of the series we were filming at any given time. I would never extend beyond where this adaptation was concerned with.

You were keeping it as immediate as you could?

Trying to, yeah.

One part of your performance that I really admired was this intricate tracing of Blackthorne getting accustomed to this culture, just in the way that you sit or the way you speak the language, and through to the respect he shows Mariko and Toranaga in the last few episodes. Can you talk a little bit about playing that?

It ends up that he has a kind of serenity about him that he doesn't have when he first arrives. It is a gradual process, and it is never a straight trajectory from the beginning to the end of how that develops, because throughout, it is pushed and pulled by external factors—frustrations that pull him back towards the man he is, and then calm him down into whatever he becomes by the end. The serenity that he has is ironically brought about by trauma, but it grants him a disassociation from things that he previously would've held quite a lot of stock in.

One of them, I think, is his life. That's not to diminish what he eventually proposes to do with Toranaga in the final episode, to say that he is himself suicidal. I'm sure he is, himself, suicidal, but it’s to do it for a purpose that’d be something that just seemed crystal-clear at that point to him. There were no remnants of his initial motivations, his quite self-interested motivations that have been prevalent throughout—in terms of his own desires and what he hoped to be when he first set off on this mission, battling the Portuguese, finding strange lands, hoping for gold, hoping for trade, hoping for notoriety, hoping to be better than Sir Francis Drake, all of these kinds of things. They're just not present by the end.

The finale opens with him having these visions of a future filled with regret, looking back. You’re in very elaborate old-age makeup. How were these sequences presented to you?

Well, the makeup was astounding. Six hours, seven hours, something like that—it took a very long time. I looked like my grandfather. It's difficult for me to talk about, because not all of that scene made it into the cut. There were parts of that scene that were not included in the final episode. Some of those omissions nailed down the nature of Blackthorne's character and motivations, as I've previously described—they nailed down the extent of them, but it was a difficult scene to play. It’s so theoretical that the purpose of that is to depict the man as he was, succeeding in the way he initially hoped to succeed, and the ramifications of that on his soul.

Was that level of physical transformation new to you?

Oh, yes, it was. I mean, they got rid of most of the scene, but to play an old version of Blackthorne, it really felt like he came full circle. It was really nice for the makeup department to allow the actor playing Blackthorne to be able to do that, because you couldn't do it otherwise. It's not the same, because you look at yourself, you see yourself in a mirror—they really imprinted some years on him.

I know it's tricky to talk about, but what do you make of what is in there versus what was cut from those future scenes?

I know the reason that it was omitted. Ultimately, it makes no difference, because it's my understanding that Blackthorne's motivations were what I thought they were since the beginning. It's clear in episode eight, when he encounters Salomon from his crew, and it's clear throughout. The sincerity of Blackthorne's arguments and pitches throughout the entire series are totally up for debate, and in terms of the motivations that catalyze them. And like so many of the other characters in the show, there's so many people who say something, but you don't know why they're saying it. The fact is, he's lying in his bed, an old man in England, and he has some Japanese artifacts, and he's told his grandchildren stories about how he killed the savages. That's what Blackthorne sees, and it terrifies him.

In the finale, Toranaga speaks in cryptic terms about his relationship to Blackthorne. At one point he says, “But he makes me laugh.” That to me felt clarifying for your dynamic with Hiroyuki and the energy between you. It made me smile.

I don't know the exact line from the piece of dialogue from the book, but yes, what Toranaga says there in relation to Blackthorne is also in the book. Well, the sentiment is there. It harks back to their initial, unspoken understanding, which was that, regardless of any of the dialogue spoken between them and regardless of any of the motivations behind it, Toranaga is using Blackthorne, to a certain extent. And I think it's fair to say that Blackthorne, to a certain extent, has attempted on many occasions to mislead Toranaga. But at the core of it, they have this unavoidable understanding and appreciation of each other's character for some reason.

The silences in the show can be quite powerful. How did you play the last look that they share? There's a kind of shared, knowing smile.

The director of that episode is Frederick E.O. Toye, he's amazing. Blackthorne was situated very far away from Toranaga for that moment, and I mean, really far away, maybe 500 meters. Toranaga appeared very small as I'm sure Blackthorne appeared to him. It wasn't really specified what the look was, and I remember Fred suggested to me the idea of a look that shared that respect and sort of admiration, but at the same time, a secondary hint of, “What are you actually doing? What’s next?” We did one of those, and I believe that's the one they ended up using—where the pureness of the initial recognition and respect and admiration is just momentarily beaten by the fact that this is actually Yoshii Toranaga, and this is probably just the beginning.

This interview has been edited and condensed.