His first series was about young men training to be come elite gangsters in a yakuza school entitled "Shiritsu Kiwamemichi Kōkō" (Ultimate Path Private High School). It was published in Weekly Shonen Jump from 1979-1980 but due to a scandal caused by an assistant sneaking real-life references into the background of two chapters, it was abruptly discontinued. The manga itself was destroyed to such an extreme extent that when it was finally collected in full thirty years later, it had to be scanned directly from old copies of the magazine.
Though this was a major event, it did not destroy Miyashita's career as he returned only a couple months later with Geki!! Gokutora Ikka which was revealed soon after its start to take place in the same universe as his first manga and all those characters became a major part of the supporting cast in his new one, even resolving some plotlines from his first manga. This was Miyashita's first shared universe and his only major work pre-Otokojuku.
He continued working in Weekly Shonen Jump consistently from the late 70's to the mid-90's and though Sakigake!! Otokojuku was by far his longest and most successful series for the magazine, he had seven serials in the magazine. Though a number of them were collected in only a few volumes, very few mangaka had this many series in the magazine's history. In time all of them would be folded into the shared universe except for the last, Bakudan.
In the mid-90's, when he left Weekly Shonen Jump, his focus shifted to Shueisha's seinen manga market, creating one of the longest-running series ever published in Weekly Playboy and several serials for the Super Jump and Oh Super Jump magazines. The Weekly Playboy series (Sora Yori Takaku) featured members of the Otokojuku cast but was not about them and his first Super Jump series was only later folded into the shared universe.
In the early 2000's in Super Jump he made his first proper Otokojuku sequel, Akatsuki!! which featured a second generation cast of the universe and in Oh Super Jump he made a long spin-off featuring the legendary Edajima Heihachi's past. These works lasted until 2010 with him ending his time in the Super Jump magazines just as they were being cancelled.
In 2011, he left Shueisha for Nihon Bungeisha where he began serializing works in their seinen manga magazine, Weekly Manga Goraku. It is these three major series that solidified the creation of a shared universe between nearly all his works. The first series was a modern remake of his very first manga (which is what inspired it to be finally collected thirty years later), the second is what combined nearly all his works into a shared universe and the third was another trip into the past of Edajima Heihachi. Though his work proper was serialized in the primary Goraku magazine, a number of spin-off's focused on individual characters by a variety of other artists have also been published by Nihon Bungeisha (most of them are serialized digitally but some in other Goraku magazines).
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