Weekly Young Jump is a seinen manga magazine, published in Japan by Shueisha since 1979. It is part of Shueisha's Jump line of comics and was launched as an older teen/young adult-oriented alternative to their incredibly popular Weekly Shounen Jump magazine.
Weekly Young Jump has published much manga of different types, perhaps most notably Lynn Okamoto, creator of Elfen Lied, Nononono and Brynhildr in the Darkness. Its stories tend to be more mature than the younger teen audience of Weekly Shounen Jump, possessing stories that can display many instances of massive violence, transgressive subject matter, and ecchi material. The covers most often feature scantily clad young women to appeal to this target audience as well.
Elfen Lied and Brynhildr in the Darkness tend to be at one end of the variations in seinen manga, which can (depending on the interpretation) even include light works like the classic romantic comedy Maison Ikkoku as well as Gantz, which compares to Elfen Lied regarding harshness of tone and content. Nononono, by contrast, fits in with other Weekly Young Jump series such as Captain Tsubasa despite its darker moments.
The weekly magazine features a postcard insert which is the notorious and awful questionnaire for various manga writers. There are several questions on both the front and back of the card (seen below).
The big one on the front reads: "Which one was most interesting? Choose top 3 from the list below. --- for this particular issue, 26 mangas, photogravures and present announcements, as well as special exhibitions, are listed. No.11 is Brynhildr in the Darkness."
The questions in the rear side read: "Which manga or articles motivated you to buy this weekly issue? Choose one out of the list in the front side." There are three more big questions that are related to photogravures (at the beginning and the ending of the magazine) and also the magazine's front cover.
Depending on the readers' responses, Shueisha, the publisher, continuously evaluates each manga and others over a period, and, in some cases, a mangaka is sentenced to discontinue their manga. In the case of Lynn Okamoto, from his tweets, we can judge he was nervous about the evaluation on at least two occasions. The first instance was a few weeks after he started Elfen Lied, and the second time was when he was forced to discontinue his second serialized manga Nononono.