Fans of the series from Japan and America combined efforts to make Fan anthologies based on the series, revolving a single character.
The first anthology was created for William Tell, who was a character in the one shot manga. Twelve artists contributed, including Hisa Masato himself, who designed the front cover of the project.
You can purchase the book here: https://theonormal.booth.pm/items/62806
The second anthology was revolved around Adam Muirhead, aka. Jack the Ripper/ Veronica Nightingale. It included twenty two artists, which consisted of light novel writers, illustrators, and manga artists. Hisa Masato included a short comic in this piece. The project also contained a two page poster spread as well.
You can purchase the book here: https://atatakaomiso.booth.pm/items/63146
The comic is R-18 for sexual content.
The third anthology revolved around the main character, Sio Ogura, aka. Nobunagun. It included seventeen artists. Hisa Masato contributed an illustration for this project as well. While the first two were created by Japanese fans of Nobunagun, this one was created by an American fan (although the majority of the artists contributing are Japanese). The prior two came out before the Anime, while this third one opened up a year after the anime aired.
You can purchase the book here: http://celebistar.storenvy.com/products/14167272-sio-ogura-anthology