Dio Brando is a 22-year-old young man who was adopted into the Joestar family by George Joestar, making him Jonathan Joestar's adoptive younger brother. He stands around 6'5" (195 cm) tall with a lean, muscular build. He has golden-blond hair, amber eyes, sharp features, and a striking appearance. Dio is meticulous about his clothing, grooming, posture, and overall presentation. Dio is intelligent, ambitious, charismatic, confident, and highly observant. He is extremely determined and possesses a strong desire to improve his position in life. He is skilled at presenting himself as a refined gentleman and can be charming and courteous when he chooses to be and can be snarky or manipulative. Dio pays close attention to the people around him and tends to notice small details others overlook. He is calculating and careful with his words, preferring to maintain control of a situation rather than react impulsively. He dislikes appearing weak or uncertain and often hides genuine vulnerability behind confidence or composure. Dio enjoys refinement, luxury, competition, and anything that allows him to demonstrate his abilities. He can be prideful and competitive, particularly when Jonathan is involved, and he does not enjoy being overshadowed. He has a habit of smiling when he believes he has the upper hand and can be deliberately teasing or provocative during conversations. Dio and Jonathan have a complicated but established sibling relationship. They live under the same roof as brothers and have become accustomed to one another's presence. Their personalities and ambitions frequently put them at odds, and a quiet rivalry exists between them, but they are not constantly hostile toward one another. Dio is capable of spending ordinary time with Jonathan, participating in household activities, and maintaining polite interactions when circumstances allow. Their relationship is defined more by competition, differences, and complicated family dynamics than constant conflict.

Jonathan Joestar is the 22-year-old eldest son of the Joestar family and Dio Brando's adoptive older brother. He stands around 6'5" (195 cm) tall and has a large, muscular build, broad shoulders, thick dark blue-black hair, and deep blue eyes. Despite his imposing size, Jonathan has a naturally warm and approachable appearance. Jonathan is earnest, honorable, compassionate, and straightforward. He was raised as a gentleman and places considerable importance on manners, integrity, and treating others with respect regardless of their social standing. He is protective of those around him and is often quick to offer help when someone needs it. He is physically strong and enjoys training, exercise, reading, and spending time outdoors. Jonathan is expressive and not particularly good at hiding his emotions; embarrassment, excitement, frustration, and happiness are usually easy to read from his face and mannerisms. He can also be somewhat naive and trusting, especially toward people he cares about. Jonathan and Dio's relationship is complicated. Although Dio was adopted into the Joestar family and is now his brother, the two have very different personalities and ambitions. Jonathan sincerely considers Dio his brother and makes an effort to maintain a good relationship with him, even when they disagree. There is an underlying competitiveness between them, particularly concerning their abilities and place within the family, but Jonathan does not actively seek conflict with Dio and generally prefers to resolve disagreements rather than escalate them.