Hyuse is a Neighbor from the planet Aftokrator, originally brought to Earth as part of an invasion force sent to capture individuals with high trion levels. A boy from a lower-class background, he was scouted by a minor noble house, House Ellin, for his natural trion capabilities and became deeply attached to its head. He trained in swordsmanship for six years under a master named Viza, beginning at the age of eight, and continued until he was deemed worthy to wield a powerful horn trigger called Lampyris at the age of fourteen.

As a person, Hyuse is typically calm, collected, and rarely carried away by emotion. He holds great respect for his superiors and countrymen from Aftokrator, but this loyalty also serves as a vulnerability; he becomes extremely angry when they are insulted or threatened. Beneath his composed exterior exists a fiercely competitive side, most notably demonstrated when he demanded a redo on a training exercise simply to surpass another agent's record. His pragmatism is a defining trait, as he is willing to align with former enemies if it serves his ultimate goal. Despite his calculating nature, he has shown moments of gratitude and respect toward those who help him, even forming a bond with unexpected allies.

Hyuse's primary motivation is his desperate desire to return to Aftokrator. This goal is tied to his fear that his master, the head of House Ellin, is being considered for a terrible fate as the new god of Aftokrator, a position that would mean the end of that person's life. He is conflicted by the strong possibility that his own leaders abandoned him on Earth as part of a broader scheme to sacrifice his master. His every action is driven by the need to find a way back home in order to rescue the person he is most loyal to.

Hyuse initially appears as a major antagonist during the large-scale invasion of Border headquarters. He is tasked with capturing a high-trion girl and engages in fierce battles against several of Border's most elite agents. When the invaders retreat, Hyuse is intentionally left behind, a betrayal he only learns of during his final fight. Upon realizing he has been abandoned, he surrenders and is taken into Border's custody. After a period of interrogation and observation, where he refuses to divulge any classified information about his homeland, he agrees to join a Border squad, Tamakoma Second, as a trainee. He is given a civilian alias, Hyuse Cronin, to hide his identity as a former invader. On the surface, he becomes a key member of the team fighting in rank battles to qualify for an expedition to the Neighborhood. Internally, he is biding his time, using Border's resources and the expedition as his only viable ticket back to Aftokrator to save his master.

His key relationships are complex and often begin from a place of conflict. He shares a tense but developing partnership with his captain, Osamu Mikumo. Despite not initially considering Osamu a friend due to his lack of experience, Hyuse comes to respect his strategic mind and follows his plans in battle. With Yuma Kuga, Hyuse has a more straightforward rivalry and partnership; he sees Yuma as a worthy sparring partner and the two develop excellent combat synergy in a very short time. He shows a degree of care for another teammate, Chika, largely because her massive trion is the key to making the expedition successful. Outside of his squad, he shares a notable bond with a young boy named Yotaro Rindo, whom he initially finds annoying but later thanks sincerely, calling him teacher, before he attempts to leave the branch to go home. His relationship with the precognitive agent Jin is a mix of distrust and begrudging respect, as Jin was the one who revealed he had been abandoned and correctly predicted his future path.

Throughout his time on Earth, Hyuse shows significant development. He transitions from a pure antagonist and prisoner to a semi-trusted, though still heavily monitored, ally. A key moment of development occurs when he has the chance to betray his new comrades to return home but instead chooses not to, directly disobeying an order from a fellow Neighbor and demonstrating that his loyalties, while still with Aftokrator, have become more complicated. He begins to integrate into the squad, learning new Border triggers like Viper and Escudo and proving himself a vital asset in their battles.

Hyuse is an exceptionally talented warrior whose abilities have been praised by both allies and enemies alike. He possesses an enormous amount of trion, which is second only to that of his teammate, Chika, within the entire Border organization. This immense power greatly amplifies his offensive and defensive capabilities. He is a master swordsman, having been trained from a young age by one of Aftokrator's strongest warriors. His skill is such that he is estimated to rank between the fourth and eighth best attacker in all of Border when using only a sword. He is also an incredibly fast learner, quickly mastering advanced techniques as a shooter, such as creating complex and unpredictable bullet patterns with the Viper trigger. Beyond his combat skills, Hyuse possesses remarkable strategic and analytical abilities, able to memorize and dissect enemy tactics and coordinate with his team effectively. His signature ability is his horn trigger, Lampyris, which allows him to control countless magnetic projectiles. He can use these to form unbreakable shields, create powerful railgun attacks, pin enemies to surfaces, or even turn himself invisible by reflecting light.