Nagare Hisui was born into a family characterized by highly formal speech and restrained emotional expression. Although their manner of communication appeared mechanical, the family maintained close bonds and could be regarded as a happy household. Nagare himself grew up mirroring this reserved style of interaction.

As a child, Nagare was present during the Kagutsu Crater Incident. On that day, he had gone to a friend’s house to play a newly released video game with his peers. While preparing to join the game, he noticed two swords suspended in the sky later revealed to be the Swords of Damocles belonging to Genji Kagutsu and Jin Habari. He pointed them out to his friends, who, believing the sight to be part of a film shoot, accompanied him to a rooftop for a better view. When Nagare observed that the red sword appeared unstable, he instinctively declared that it would fall. Moments later, the red Sword of Damocles crashed to the ground, triggering the Damocles Down. The resulting shockwave devastated the area, killing his friends and nearby families. Though struck by falling debris that pierced his chest, Nagare survived becoming the sole survivor in the immediate vicinity.

Nagare was later discovered amidst the destruction by Tenkei Iwafune. In that moment, his powers as the Green King awakened, and his Sword of Damocles manifested, preserving his life.

At some point, Nagare challenged the Gold King, likening the confrontation to facing a “final boss.” Though powerful enough to rival the Gold King, he was ultimately defeated. Following this event, his direct activities as a King diminished, and he began operating primarily through his clan, the Green Clan, issuing missions via its digital platform while entrusting much of the work to his Clansmen.

Nagare also attempted to test the mortality of newly awakened Kings by ordering Hirasaka Douhan to assassinate Reisi Munakata. The attempt failed when Zenjo Gouki deflected the bullet with his sword.

In later years, Nagare is depicted confined to a wheelchair due to a permanent disability. He is also shown to be aware of Neko’s past, referring to her by her original name, Miyabi Ameno, and remarking on their similarities.

Nagare is a pale-skinned young man with messy, neck-length dark green hair, with bangs falling over the left side of his face. His eyes were originally both blue, but following his awakening as a King, his left eye became filled with green light from his Aura. Where his heart should be, there exists a cavity that is sustained by his Aura, functioning as a substitute life force similar to a core of energy.

For much of the series, Nagare is depicted restrained in a teal straitjacket, left unfastened only at the bottom. The garment has a tattered hem that exposes yellowed leg restraints, and he wears dark blue strapped sandals. These restraints are designed to suppress and regulate his immense power. He is seated in a technologically equipped wheelchair, primarily white, blue, and black in color, fitted with various controls such as colored buttons, a red triangle, an inverted blue triangle, and a green square their precise functions unknown. A digital pad often rests across his lap.

When Nagare unleashes his powers, his appearance alters dramatically. His Aura shreds the straitjacket, revealing flowing white garments beneath. His attire includes a shirt with an upturned collar, loosely sewn sleeves held together by criss-crossed blue stitching, and ruffled ends, with similar stitching visible on his back. He also wears white trousers overlaid with a robe or skirt, and completes the look with a long, uneven scarf that extends past his knees. In this state, his hair glows a brilliant white, while his left eye turns green and both eyes develop slit pupils.

After the Dresden Slate’s release, Nagare’s hair permanently remained white due to the surge of power, and his outfit shifted to a darker variant resembling his previous white attire. His clothing appears white whenever his Aura is active, but following the Slate’s destruction, both his hair and clothing returned to their original dark green and black.

Nagare Hisui is depicted as a complex figure, blending the traits of a manipulative strategist, an idealistic visionary, and a childlike dreamer. Unlike Kings such as the Red or Blue, who cultivate strong, loyal bonds with their clansmen, Nagare treats many of his subordinates as expendable assets in pursuit of his goals. He entrusts them with dangerous missions, sometimes with little regard for their survival, as seen when he activated jungle’s explosive devices despite knowing Douhan Hirasaka remained in the blast radius. This tendency suggests that he views his Clansmen either as capable individuals who should manage on their own or as tools necessary for advancing his ambitions.

Despite this harsh pragmatism, Nagare shows warmth and respect toward his J-Rank Clansmen. He treats Tenkei Iwafune as a father figure, openly supports Sukuna Gojo’s enthusiasm for video games, and entrusts major operations to Yukari Mishakuji, who often disciplines Sukuna when he is distracted. His relationship with the three J-Ranks is informal and familial, as demonstrated by his suggestion that the clan should hold a Christmas celebration after acquiring the Dresden Slate. He also relies heavily on Kotosaka, using the bird as both a companion and a surrogate presence in the outside world due to his physical disability.

Nagare’s intelligence allows him to manipulate others, most notably the Colorless King, whose actions sparked widespread chaos after being influenced by Nagare’s advice. While he is aware of how easily he can sway others, he insists that manipulation is not his intent. Nonetheless, he demonstrates no hesitation in ordering his top Clansmen to kill or eliminate threats to his plans.

Beneath his cold pragmatism lies a distinctly childlike outlook. Nagare frames his ambitions as though he were “playing a game,” pursuing them with sincerity and enthusiasm. He genuinely believes his vision will lead to positive outcomes, harboring no malice even when acknowledging the potential risks. His dream is of a world where every individual possesses freedom and power, accepting the “natural selection” this would entail. He displays an open and honest manner, answering questions without hesitation even when speaking with enemies such as Anna Kushina or Adolf K. Weismann, and is quick to welcome new members who reach J-Rank within jungle. He admires creativity and unorthodox thinking, encouraging those who “play the system” rather than condemning them.

Nagare respects Adolf K. Weismann above all other Kings, recognizing him as the only one he acknowledges as his superior. His reverence for the Silver King motivates much of his strategy, including the abduction of Anna Kushina to exploit her divination powers in locating Weismann. His respect does not prevent conflict, however, as when Weismann refused to cooperate in Nagare’s plan to unleash the Dresden Slate’s power for humanity’s evolution, Nagare immediately declared war against him. The exception to his ruthlessness is Neko, whom he identifies as similar to himself, an extraordinary being whose identity has been profoundly shaped by her powers and whom he insists must not be harmed.

Overall, Nagare embodies the paradox of being both an innocent dreamer and a ruthless tactician. While his methods often unsettle his followers and enemies alike, his sincerity, honesty, and unwavering belief in his vision distinguish him from other Kings.

Green Aura
As the Green King, Nagare wields a highly destructive Aura that manifests with electrical and ray-like properties. Following the Kagutsu Crater Incident, in which he lost his heart, Nagare was freed from what would have been his natural physical limitations. This allowed him to push his powers to their extreme, granting him strength great enough to rival even the Gold King. However, his life is now sustained entirely by his Aura, leaving him with a finite time limit during which he can maintain full strength. Once this limit is exceeded, he is left severely weakened, possessing only enough power to keep himself alive. Despite this drawback, Nagare is regarded as one of the most powerful Kings, both in combat ability and influence. His use of power is accompanied by a surge of exhilaration, often displayed through feral, almost cat-like expressions.

Mediumship
Nagare is capable of extending his consciousness into Kotosaka, a green parrot who serves as his medium. Through Kotosaka, Nagare can perceive the outside world, speak with others, and issue commands. When acting as his vessel, Kotosaka’s eyes glow bright green and his voice shifts to Nagare’s own.

Transformation
When unleashing his full Aura, Nagare undergoes a transformation that releases immense amounts of energy. This state, referred to by Anna Kushina as a “Lightning Beast,” allows him to take on a form of living lightning capable of moving at extraordinary speeds, possibly exceeding the sound barrier.

The given name Nagare (流) can be translated as “style,” “manner,” or “method.” His surname, Hisui (比水), is composed of the characters 比 (hi), meaning “ratio” or “comparison,” and 水 (sui), meaning “water.”