Ata Ibusuki holds the position of second-year student council president at Binan High School, widely respected for his academic excellence and composed demeanor. Maintaining this reputation demands significant personal effort. His physical appearance features long bluish-violet hair tied in a ponytail, crimson eyes, and a slender build. He wears a distinct school uniform variant: a white blazer with gold accents, a gray vest, and a black shirt. When transformed into the magic knight Ritter Diamant under Prince Furanui's influence, his attire shifts to a dark blue Arabian-inspired suit with black and gold details, a lilac breastplate, and a black-and-red cape, wielding a large sword. This transformation, achieved through the Druck ring, symbolizes his association with the element of violet diamond.

Ata's personality centers on a rigid adherence to order and structure, driven by a deep-seated need for control. This rigidity traces back to childhood experiences where he consistently ranked second in competitions, overshadowed by his classmate Kyoutarou Shuzenji, whose natural talents allowed him to excel effortlessly. For instance, Ata practiced diligently to master skills like pen spinning or clearing six gym mats, only for Kyoutarou to outperform him casually, fostering enduring resentment. His inflexibility was cemented by an elementary school incident: visiting a bathhouse with Kyoutarou and Ryouma Kirishima, he panicked upon encountering unfamiliar customs and fled, later distancing himself from both friends due to feeling betrayed by their lack of guidance.

Ata's background reveals a sustained rivalry with Kyoutarou. Flashbacks show his bitterness over repeated losses, such as Kyoutarou winning first place for a hastily painted fruit bowl while Ata's meticulous work placed second. Despite occasional childhood camaraderie, like playing in mud, Ata's envy festered, leading to estrangement. Years later, Prince Furanui—a fennec fox seeking to conquer Earth—identified Ata's seriousness and resentment as exploitable traits. Though initially coerced, Ata voluntarily joined Furanui's Edelstein knights in exchange for a share of the prince's magical power, viewing it as a tool for achieving superiority. As Edelstein's commander, he collaborated with Taiju Unazuki and Maasa Shirahone to target emotionally vulnerable students, transforming them into monsters to spread discord.

Ata's development culminates in a confrontation with Kyoutarou, now a member of the rival Happy Kiss group. When Kyoutarou belatedly invites him to the bathhouse to mend their friendship, Ata's pent-up fury resurfaces. Furanui exploits this, transforming him into the Black Knight—a winged, masked entity radiating purple energy and consumed by negativity. In this state, Ata attacks Kyoutarou, who refuses to retaliate and instead offers a sincere apology and embrace. This act dismantles Ata's monster form and resolves his longstanding resentment. Though their reconciliation is interrupted by an emergency involving King Kamopapa, Ata is shown reconsidering his hostility.

Outside these conflicts, Ata prefers solitary activities like spending time at home and enjoys nagashi-somen. His name reflects his traits: "Ibusuki" references a hot spring in Kagoshima Prefecture, while "Ata" translates to "full," implying weariness or frustration.