Don Bonby serves as the public alias for Kintaro Asechi, an elderly fashion designer and the series' primary antagonist. Operating as Don Bonby, he founded the Symphonia Company and created the Symphonia Series clothing line, using this identity to monitor Prism Shows at Pretty Top and manipulate talented Prism Stars. His distinctive Don Bonby appearance features nose-and-mustache glasses, and he utilizes multiple lookalikes to preserve his cover across various locations.

Kintaro's past is marked by personal betrayals. In his youth, he collaborated with Myeong Ja on wedding dress designs such as the Pure White Wedding Dress and Romantic Night Wedding Dress. He abandoned her after witnessing Kei perform the Aurora Rising, subsequently marrying Kei. This marriage ended in divorce when Kei departed to protect herself and their daughter, Kyoko Asechi, from Kintaro's intensifying fixation on the Symphonia Series. This obsession stemmed from his ambition to revolutionize Prism Shows by replacing traditional competitions with the ultimate "Grateful Symphonia" Prism Act.

Employing the Don Bonby alias, Kintaro orchestrated schemes to achieve his goals. He sabotaged P&P's second show by leaking Aira Harune's outfit plans to Hye-in and later gave Aira a Symphonia Series stone, brainwashing her into joining his company. His manipulations forced units like MARs, Serenon With K, and Love∞Mix to defect. During the Sky High Symphonia tournament, any Prism Star losing to MARs faced a contractual obligation to join Symphonia Company. When Kyoko fell critically ill, Kintaro paused his agenda to cook with Prizmmy☆ and PURETTY, revealing residual familial concern before his memory deteriorated.

Kintaro's downfall commenced after PURETTY and Shou reversed his brainwashing of Aira. In retaliation, he publicly exposed his financial manipulation of Kyoko's rise to Prism Queen, triggering a collapse in public trust for Prism Shows. During the final Grateful Symphonia performance in Buenos Aires, he attempted disruption but was confronted by Mia Ageha. She articulated how rivalries and friendships fueled her growth, persuading him to abandon interference. The successful performance restored Prism Shows' reputation.

Following these events, Kintaro retired from fashion design. He became a farmer at Kei's estate, symbolically hanging his Don Bonby costume on a scarecrow. Despite this redemption, he retained traces of eccentric behavior. His relationships remained unresolved; while he reconnected with Kei and Kyoko, his past abandonment of Myeong Ja indirectly influenced the arrival of the Korean transfer students, including Yun-su and Chae-kyoung (Myeong Ja's children).