Though it is one of the very few manga publishers to have been founded before the 20th century, the publisher actually had very minimal association with manga for the first hundred years of its existence. Better known for literary and news related magazines like Shinchō (begun in 1904) and Weekly Shinchō (begun in 1956), their first major step into manga only came about in 2001 with the launch of the manga magazine, Weekly Comic Bunch.
Though Shinchosha published the magazine and its collected serials, the actual launch of the magazine and the Bunch Comics line was through the Coamix company, founded by and based around a group of successful alumni of Weekly Shonen Jump (which less than ten years earlier had been at its commercial peak with many of these same creators but in 2001 was no longer the top-selling manga magazine in Japan and was mostly dominated by then-rookie creators).
So, in the early issues of the new Comic Bunch magazine, serials were launched by a number of creators from Jump's late 80's/early 90's era including those by the founders Tsukasa Hojo, Tetsuo Hara and Ryuji Tsugihara but also serials by other famous Jump authors from the past like Koji Koseki, Shinji Imaizumi, Makoto Niwano, Satoshi Ikezawa and a few years later, Go Nagai. Built heavily around this Jump nostalgia, the two headlining series were direct spin-offs of major successes from Jump's Golden Age with Angel Heart being spun-out of City Hunter and Soten no Ken from Hokuto no Ken.
The magazine continued on through the decade and would continue serializing new works based on these founding author's previous works (such as five different, often simultaneously published, side-story serials about side characters from Hokuto no Ken, each by a different artist) but it also gained some new creators that weren't part of this Jump history who started serials like Btooom! and Uroboros.
So in 2010, when Weekly Comic Bunch ended and Coamix's partnership with Shinchosha had stopped, there was left a group of creators still tied intrinsically to the works of Hara and Hojo and Shonen Jump and new creators who were working on serials unrelated to that era. As a result, Weekly Comic Bunch was ultimately revived as two magazines; Monthly Comic Zenon (published by Tokuma Shoten, who were the new partner of Coamix) and continued publishing spin-off's to Jump classics and Monthly Comic@Bunch which was Shinchosha's new manga magazine to continue on the Bunch Comics line with the creators from Weekly Comic Bunch that weren't as bound to Coamix.
Interestingly, one of the first brand new series launched in Comic@Bunch (in the second issue) was by Man☆Gatarō, who was one of the most significant (but controversially non-mainstream) creators to debut in Jump during the exact era many of the creators who established Weekly Comic Bunch were from.