Three years prior to the events of the series, Hiroomi attempted to subjugate Akihito Kanbara under the orders of his cousin, Izumi Nase. During this mission, Akihito was gravely injured by Miroku Fujima, triggering the awakening of his Youmu side. In his transformed state, Akihito nearly killed Hiroomi, an event that established the need for the Nase family to monitor him closely.

In Beyond the Boundary Movie: I’ll Be Here – Future, Hiroomi is depicted as having succeeded Izumi as the head of the Nase household following her disappearance. His appearance in the film reflects this transition, as he dons a black trench coat while retaining his signature scarf. By this time, his skills as a Spirit World Warrior have advanced significantly, particularly in his mastery of barrier techniques, such as creating large-scale barrier cages.

Hiroomi is a young man of average height with a slender build. He has a bowl-cut hairstyle of black hair, with bangs that fall over his eyebrows, and striking green eyes.

He is most often seen in his school uniform, typically accompanied by a red-and-black scarf or muffler, which he wears due to his sensitivity to cold. In Beyond the Boundary Movie: I’ll Be Here – Future, he is shown wearing a formal suit, reflecting a more mature appearance.

Hiroomi presents himself as calm, composed, and often mature in comparison to those around him. He carries out his duties as a Spirit World Warrior with seriousness and reliability, frequently acting as a mediator between Akihito Kanbara, Mirai Kuriyama, and his younger sister Mitsuki. Despite his usually level-headed demeanor, he has a mischievous side, often teasing Akihito by calling him “Akkey” and engaging in playful antics that contrast with his otherwise stoic image.

A defining aspect of Hiroomi’s character is his pronounced sister complex, as he openly dotes on Mitsuki to an excessive degree. While this behavior often embarrasses her, it also underscores his deep attachment to his family. Beneath his teasing and eccentricities, Hiroomi demonstrates a strong protective streak, especially toward Mitsuki, and takes his responsibilities as both her elder brother and a member of the Nase family seriously.

Hiroomi inherits the distinctive abilities of the Nase family, specializing in barrier techniques and unique spiritual weaponry.

Glaciate Barriers
Like his relatives, Hiroomi can create Glaciate Barriers, defensive constructs capable of restraining or obstructing Youmu. His barriers proved resilient during the appearance of the Hollow Shadow, though they were ultimately ineffective against Akihito Kanbara’s Youmu transformation.

Scarf Weapon
Hiroomi’s signature ability is the use of his enchanted scarf, which can disintegrate Youmu upon contact. He wields it both offensively and defensively, employing it to slice through opponents or trap them before eradicating them. This power is directly tied to his heightened sensitivity to cold, requiring him to constantly wear a muffler or scarf to regulate his condition.

While skilled, Hiroomi occasionally struggles to remain composed in combat when distracted, particularly if his younger sister Mitsuki expresses concern for him.

Mitsuki Nase
Mitsuki is Hiroomi’s younger sister, and their relationship is marked by frequent bickering that quickly gives way to reconciliation. Hiroomi openly exhibits a strong sister complex, blushing or even suffering nosebleeds when Mitsuki affectionately calls him onii-chan. His cellphone ringtone is a recording of Mitsuki saying, “Onii-chan, I love you.” Despite this eccentric attachment, he genuinely loves his sister and goes to great lengths to protect her from harm, sometimes keeping secrets from her to spare her from worry.

Akihito Kanbara
Hiroomi was originally assigned to kill Akihito after his Youmu side surfaced, but the two eventually became close friends. Their bond is often portrayed humorously, with Hiroomi teasing Akihito by placing his hands under his armpits, a recurring gag that frustrates Akihito and once led Mirai to jokingly question if they were romantically involved. Beneath the humor, Hiroomi cares deeply for Akihito, refusing Izumi’s later order to kill him by replying, “Like I could kill him.” In Beyond the Boundary Movie: I’ll Be Here – Future, Hiroomi and Mitsuki are shown overjoyed at Akihito and Mirai’s return, with Hiroomi leaping onto Akihito in relief.

Izumi Nase
Hiroomi’s relationship with Izumi, his cousin and head of the Nase family, is rooted in respect but strained by her strict views on duty. He once admired her as an idol, but by the end of the anime series, he renounces her path, declaring that he does not want to become like her. In Beyond the Boundary Movie: I’ll Be Here – Future, Izumi is revealed to have been overtaken by a parasite-type Youmu, becoming the hooded figure attacking Spirit World Warriors. Hiroomi, alongside Ayaka, confronts her but initially struggles due to his lingering love and respect for her. In their final confrontation, he admits that he should not have blindly chased after her ideals, but instead should have supported her as family. The siblings ultimately reconcile before the film’s conclusion.

The given name Hiroomi (博臣) combines hiro (博), meaning “command” or “esteem,” and omi (臣), meaning “minister.” It can also be interpreted as “acclaimed attendant,” aligning with his description as a “watchman” in his official character profile.

His surname Nase (名瀬) is composed of na (名), meaning “name,” “noted,” or “distinguished,” and se (瀬), meaning “swift current” or “rapids.” The surname can be understood as “renowned position,” reflecting the high standing of the Nase family among Spirit World Warriors.