The first story arc of JoJo's Bizarre Adventure was the Phantom Blood storyline, which was rather straightforward compared to later arcs, like Stardust Crusaders and Golden Wind. Still, the series had to start somewhere, and played it safe with a conventional shonen hero, Jonathan Joestar. Jonathan had an equally conventional villain to face: Dio Brando.
Jonathan and Dio met as boys, and when they were young men, they faced off as mortal enemies over the fate of the entire Joestar family. Jonathan gave his life to stop Dio's rampage, but before that point, he had a rather interesting relationship with his foster brother.
Jonathan & Dio Are Two Side of the Same Coin
It was clear from the very start that Jonathan and Dio were destined to be enemies, even if they got along as foster brothers on the surface. Jonathan was a bit bratty around age 12, but still had the heart of a hero. He put others first and wanted to live up to other people's expectations of him. Jonathan was a heroic figure in that sense, and since he belonged to the esteemed Joestar family, even more expectations were piled on him. Jonathan was very much connected to other people, drawing inspiration and courage from them. He would feel the same way when he met Baron Zeppeli, who taught him the power of Hamon/Ripple.
All that contrasted starkly with Dio, who came from nothing and aspired to be everything. He only had his drunk, bitter father Dario for family, who Dio scorned after his death. Dio thought only of himself, and would spite anyone who got in his way, even those he should've sympathized with. Dio's interests all went inwards, not outwards, immediately straining his relationship with Jonathan, who could hardly even conceive of deception or manipulation.
Put simply, Jonathan was innocent and Dio exploited that right away. He tormented Jonathan behind George Joestar's back, though Jonathan gave Dio many chances to turn over a new leaf and become a gentleman. But eventually, Dio pushed Jonathan too far, and Jonathan retaliated, finally recognizing Dio as an enemy. Behind the scenes, the two brothers were proper enemies, and they both hid this fact from society at large. They even cooperated during a football game, and paid each other elegant compliments.
The two of them were light and darkness, and the darkness was attempting to drag the light down with it. Dio wanted to bring Jonathan down to his own level, then crush him, but Jonathan didn't let that happen. He had different sentiments toward his hostile foster brother.
Dio Pushed Jonathan to the Brink
Another theme to the relationship between Jonathan and Dio is the temptation of power and wrath. Given the right provocation, even the best of people may succumb to their darker feelings, especially if they have little to lose. Dio provoked and tormented Jonathan nonstop, and although Jonathan struck back with his fists, he still sincerely believed that there was still good in his foster brother. Jonathan wanted to fix their relationship until the moment Dio became a vampire, and he tried to reach out to Dio's good side (or what little of it was left) and bring it forth. Aside from a few fistfights, Jonathan resisted the temptation to sink to Dio's level, and he walked the high road in their relationship.
So, Dio took the next step and donned the stone Aztec mask, becoming a vampire and causing George Joestar's death. Jonathan, having little left to lose, learned the ways of Hamon, faced Dio one more time and defeated him. Dio's severed head was kept in a storage box as Jonathan and his wife Erina sailed to the United States, and Dio struck once again. What came next wasn't just an exciting battle — it also revealed the final phase of the pair's relationship.
Dio, desperate, offered to lend his powers to Jonathan and save his life with vampiric immortality. Jonathan refused and instead held Dio's head to his chest as he lay dying, with the ship burning to pieces around them. Jonathan still loved Dio as a brother, and he wouldn't ever let go of that bond that connected them. This shocked and infuriated Dio, and he was still cursing Jonathan as he passed away and the ship fell apart. Dio had failed one last time to corrupt and twist his foster brother, and his relationship with Jonathan ended with Dio's failure — on multiple levels. The light in Jonathan wouldn't be snuffed by darkness so easily.
