They arrive unexpectedly, flickering moments that make you unsure if you are peering at a video game or the real world.

Cold sunlight that causes wet rocks to turn blindingly bright. Undulating hills slinking off into the misty nothingness of the horizon. The nearly photorealistic face of Senua, the unconventional hero of this 10th-century revenge tale, as she grimaces with every sinew taut, her veins bulging.

The verisimilitude of Senua’s Saga: Hellblade II, which releases on Tuesday for the PC and the Xbox Series X|S, is so exact, cutting-edge and convincing that it seems possible for players to entirely suspend their disbelief.

One could argue that this hyperrealism is paramount for a third-person action game that presents a pictorial realm of visions and wonders, of fire-breathing humans and slithering giants. Yet these folkloric flourishes are grounded by earthy, authentic details like the flecks of muck and gore that accumulate on the characters.

“The goal is to move people,” Dom Matthews, the 40-year-old leader of the game’s developer, Ninja Theory, said from its plush studio in Cambridge, England. “Our belief is that we do that through delivering an experience that is believable. When someone forgets that they’re in a video game level and is focused on the narrative journey of Senua, then they’re opened up to be moved emotionally.”

The first Hellblade game, Senua’s Sacrifice, took place in the immediate aftermath of catastrophe: Vikings had murdered Senua’s village on the Scottish archipelago of Orkney and sacrificed her lover, Dillion, to Norse gods. Players directed Senua to the underworld of Helheim so she might save his soul.

In the sequel, Senua’s purview is expanded as she makes her way across the stormy North Sea to Iceland, intent on tracking down those responsible for his death.

The franchise’s emphasis on authenticity and realism extends into the singular phantasms of its protagonist, who suffers from psychosis. The turbulent mental state of Senua, played with fierce, haunted intensity by Melina Juergens, often manifests in disconcerting ways: chattering internal voices that swirl around her in 3-D audio and wraithlike enemies that are figments of her imagination.

Alongside this interior landscape, Ninja Theory has gone to extreme lengths to achieve believability for the physical world, basing a huge proportion of its in-game material directly upon real-world sources through a process it calls “capturing reality.” The intensively motion-captured combat system was the product of 70 grueling days with a stunt team, and field recordings were gathered in Iceland, Scotland and Wales.

The rough terrain Senua walks upon, plotted with huge volcanic rocks blotched with fluorescent lichen, was stitched together from satellite imaging, drone footage and photogrammetry, said Chris Rundell, an environment artist. The team took thousands of photos of stones, trees, shrubs, traditional turf houses and tiny Viking-esque statues they had carved themselves before scanning them into the computer.

“You get a perception of the scale of the place, but also how things feel, sound, smell,” said Rundell, who wanted to impart his own experience of Iceland — the bludgeoning rain, the softness and harshness of the mossy, craggy ground — onto the game. “Being there, and being able to touch that stuff, you carry it back with you.”

Dan Crossland, a character art director whose unkempt hair and dark beard would make him a perfect extra in a medieval movie epic, spoke proudly of commissioning real costumes for Senua and other characters from an artist in London. On display in one of the studio’s many lounge areas, which are also filled with reference books for subjects like art history and programming, these costumes were constructed from leather, cotton and hemp using period-appropriate techniques like weaving. Crossland then scuffed up and even burned the outfits to make them feel more lived-in, hoping to evoke the “raw, broken-down state” of life in 10th-century Iceland.

“There’s nothing too gamey about it. It’s just matter-of-fact: what materials they had, what was available,” he said. “It’s a survival thing.”

Senua’s Saga takes place around the time that the Althing, the Icelandic parliament, was founded in 930. This was a place of “isolated communities,” said the scriptwriter Lara Derham, one where “folklore and religion were densely woven into societies and into the land itself.” Senua has a predilection for seeing runic patterns in the environment, crucial for solving puzzles and unlocking the path forward.

These runic puzzles tap into the “horrible, bubbling sense of uncertainty” that those experiencing psychosis can encounter, said Paul Fletcher, a professor of neuroscience at Cambridge University who advised Ninja Theory on both Senua games.

Fletcher does not believe that it is anachronistic to speak of psychosis in the medieval period, noting a “quite surprising level of sophistication” in which people then talked about mental illness and, specifically, madness. There are classification systems within historical documents, he said, that reveal a “compassionate approach to understanding people.”

“It would often entail things like being thrown into turmoil by grief or battle terror,” he said, “or going off into the wilderness with a quest in order to expiate your sins.”

For a game that foregrounds such a subjective perspective, the idea of “capturing reality” might appear a strange, even paradoxical, approach. Yet it offers something like a base line over which the game’s designers and artists have added impressionistic layers of sparkling and shimmering mental perception. The moon shines just a little more intensely; the colors of Iceland’s primordial landscape appear just a touch more vibrant; particles and debris billow in the air dramatically. It is a world of vivid hyperreality through the eyes of a character whose cognitive faculties seem to function in overdrive.

Fletcher sees these elements as consistent with Senua’s mental state. “Very often in psychosis, people feel incredibly close to natural occurrences,” he said. Even time itself is changed, an eerie dusk segueing into bewitching night in what feels like the blink of an eye.

These details add up to a strikingly aestheticized adventure, one that seamlessly blurs the boundary between the imaginary and real. The protagonist’s slippery grasp of reality and the ravishing visuals that move beyond the “uncanny valley,” the result of both sheer polygon processing power and deft artistry, arguably push Senua’s Saga as close to photorealism as the interactive medium has come. It is tricks of the mind all the way down.

Yet this simultaneously visceral and illusory experience is rooted by Senua. With her subconscious splayed onto the screen with terrifying and beatific aplomb, Matthews said it was vital she remained a believable person.

“In the same way that we’re translating a real-life costume into the game digitally, we’re trying to do the same with the reality of people’s experiences and that of neuroscience,” Matthews said.

The aim is for the player to feel both the full force of distance between themselves and Senua, a 10th-century woman with a remote belief system, as well as an intimate and often uncomfortable closeness.