Shinseiki Evangelion: Koutetsu no Girlfriend 2nd is based on Gainax's visual novel of the same title. While the first four volumes are an adaptation of the game, the final two are exclusive stories based on the characters in the game.
The series was published in English as Neon Genesis Evangelion: Angelic Days by ADV Manga from May 16, 2006 to August 21, 2007.