Akira was caught in Keicho Nijimura's crosshairs—literally. While Keicho hunted for a Stand user powerful enough to kill his mutated father, he fired his supernatural Bow and Arrow at random people, and Akira happened to be one of them. Unlike most of Keicho's victims, Akira actually survived the encounter and awakened a Stand in the process. That brush with death sparked an obsession: he became fascinated with Stands themselves and the mechanics of how they were created.
With his newfound power, Akira's interest turned darker. He started harassing people around town, including Josuke, as he experimented with his Stand and tried to level up his guitar playing at the same time. It's unclear how much genuine musical ambition drove him versus how much was just an excuse to mess with people, but either way, his behavior made him a pest to anyone unlucky enough to cross his path during this phase.
Content compiled by AnimeList.moe from publicly available sources.