Asuka has short, purple hair, with the middle section of his bangs resting on his nose, and the rest above his eyes. His eyes are olive green. He can either be seen wearing the blue HOLY jacket and matching pants with black knee-length boots, or a red undershirt and beige coat.
Asuka has a sweet demeanor when he's not fighting, but when conflict arises he becomes stern and professional. Early in the series, a bitter but unrequited rivalry with Kazuma rises after he is embarrassed by Kazuma during his escape from HOLD headquarters.
In the manga he is quite different in the beginning, he believed that the people in the Lost Ground deserved to suffer, since he lost his family to them, due to him being an Alter User. He also constanly makes perverse comments, such as his Eternity Eight being his balls & the like.
But when he's assigned to follow Mimori Kiryu, he gets the shock of his life. He runs into Kazuma, the Native Alter who had been giving HOLY such a tremendous headache. Asuka fights Kazuma, but he loses, and his right arm is broken in the process.
Because of his loss, not only is he removed from the ranks of HOLY, but he loses contact with Cammy. The triple whammy of losing the fight, his prestige, and his girl drive him crazy, and this makes him interfere in Kazuma and Ryuho's second encounter. In the ensuing upheaval, he and Kazuma become trapped underground.
Forced to work together, Asuka finally gets a clear picture of what makes Kazuma tick. He realizes that Kazuma isn't crazy, just fighting with an implacable resolve. He also realizes why Kazuma is fighting: because HOLD and HOLY are intruding on the Inners and he's just defending his turf. Asuka begins to realize that his own resolve had never been that strong. He'd been hiding behind that HOLY badge when he should've been trying to earn that privilege.
From then on, Asuka resolves to earn his keep. Unable to return to HOLY, he takes up a job as a smuggler, stealing supplies from within the city to take to the Inners on the outside. He eventually makes contact with Mimori when he rescues them from a group of thugs. After the Second Uprising, the two continue working together, their mutual concern for Kazuma and Ryuho keeping them going.
But when Asuka sees Kazuma again after the Uprising, he sees Kazuma a bitter man who's turning his back on his past. He tried to snap him back to his senses, but it doesn't work - right away, at least.
Eternity Eight: The manifestation of Asuka Tachibana's "Alter". "Eternity Eight" typically takes the form of 8 small, bright green orbs which freely levitate around his body. Through these orbs, Tachibana has the ability to freely manipulate the flow of life-force through a particular medium. This typically means through contact with living organisms (at least as high as humans in complexity), but also the orbs can produce their own effects by presumably consuming Tachibana's own energy reserves. As a result of its general manipulation, Tachibana's "Eternity Eight" is an extremely versatile weapon and tool, both inside and outside of combat. He also seems able to track to an unknown distance, as he's used them to track Kazuma & Kimishima.
- Mind Control: The "Eternity Eight" orbs are capable of forcefully embedding themselves into the flesh of living organisms, rendering their minds unconscious and possessing the bodies for usage as puppets under Tachibana's control. Up to 8 bodies can be controlled at any one time, coinciding with the number of orbs, and living organisms as intelligent as fellow humans can be easily tamed by the power. Multiple orbs can also attach onto a single individual, amplifying the power (against opponents with greater mental fortitude than average) at the cost of reducing the quantity of "mindslaves" available and restricting Tachibana's options in combat.
- Ring Platform: Through the usage of at least 4 "Eternity Eight" orbs, Tachibana can transmute them into a ring of energy, which he can then rest upon and fly across the air at high velocities. He can also use this on enemies to raise them off the ground & prevent them from attacking him.
- Luminence: Tachibana can cause an "Eternity Eight" orb to radiate a bright yellowish-green glow, illuminating dark surroundings.
- Healing Boost: By embedding an "Eternity Eight" orb into an ailing individual, Tachibana can accelerate the rate of their natural healing factor to cure their conditions quicker.
- Eternity Eight: Ring: By arranging an unknown amount of orbs in a tight circle around the opponent, he can generate a circle of solid green energy construct to bind the enemy or simply lift them of ground to keep them from attacking.
- Eternity Eight: Shield: By concentrating the strength of all 8 orbs into a minimized orbit, Tachibana can generate a flat "barrier" effect that screens him from incoming powers (it was able to deflect the majority of Kazuma's "Shocking First Bullet" energy into simply launching Tachibana into the air, rather than cause any harm, as well as an incoming strike from the refined "Hammer" Alter of Biff's).
- Eternity Eight: Sword: This is the primary offensive augmentation that Tachibana uses in combat. Arranging all 8 orbs in a vertical formation, Tachibana then generates a solid energy construct around the array to enable him to wield the "blade".
- Eternity Extra Shot: Tachibana's most dangerous technique with the "Eternity Eight". He deconstructs further material in his vicinity to form a heavily stylized bow attached to his left wrist, then sets each orb in the gaps between the bow's spines. He then aligns all 8 orbs in a tight formation (like that of "Eternity Eight: Sword") before firing it from the bow towards the opponent. With all 8 orbs striking the target's head, Tachibana states that "Eternity Extra Shot" is designed to overload the mental faculties of the victim and essentially erase their mind.
Eternity Eight: Asuka's Eternity Eight seems to be a good deal different from its anime-counterpart. It allows to the user to show the memories of those it comes in contact with & is able to brainwash people. They can also be used to physically attack people.
- Eternity One: Asuka combines all of the Eternity Eight into one giant orb. It possess a good amount of physical power.
- Eternity Twin: Asuka creates a second Eternity One.
- Eternity Twin: Mind Control: Asuka uses Eternity Twin to take control of the targets mind.