I'm not sure this is what they meant when they said Shonen Jump and Shonen Magazine carry some of the biggest manga titles.

Publishers Shueisha and Kodansha have merged their magazines for one truly gigantic issue as part of the joint "Shōnen Jumaga Gakuen" project. The commemorative issue includes 2,264 total pages with a 13-cm wide spine. Inside are opening chapters for 44 individual manga series from Weekly Shonen Jump and Weekly Shōnen Magazine .

An even larger version is available to read online. The digital version includes the first chapter of 71 manga series, including series from Kodansha 's Bessatsu Shōnen Magazine .

A total of 120 characters from the magazines will appear in a 30-meter advertisement in Shibuya station from May 6 to 12.

Kodansha and Shueisha opened a site for Shōnen Jumaga Gakuen on April 8. The website asks for participant's date of birth and is only open to readers under the age of 23. The website frames itself as an actual school where all the learning materials are manga magazines.

Source: Comic Natalie