Shingeki no Kyojin: Kuinaki Sentaku

A spin-off shoujo manga that centers around Levi's and Erwin's past. The young Erwin Smith is a rising star in the Survey Corps, humanity's only hope of defeating the man-eating monsters known as Titans. Ruthless and dispassionate, Erwin's mind is devoted to strategies and intrigue. But beneath Erwin's feet is another world, the "Underground," where humans are born and die surrounded by the garbage the Capital throws away. Here, the criminal Levi survives on his wits and agility. But when these two ambitious men cross paths, who will prove himself stronger? (Source: MU)

Shingeki no Kyojin: Kuinaki Sentaku is based on the visual novel of the same name. The visual novel was bundled with the first press release of the sixth Blu-ray volume of the anime's first season and was supervised by Shingeki no Kyojin creator Hajime Isayama. The series was published in English as Attack on Titan: No Regrets by Kodansha Comics USA from June 24, 2014, to October 28, 2014, and again in a full color omnibus. It was also published in Spanish by Norma Editorial from October 30, 2014, to March 20, 2015; and in Russian by Azbuka in a complete omnibus on March 10, 2017.