FHD Remix is a fanfiction novel combining the three worlds of Featherwing Love (by Terry Wilson, user fhd_remix here), Haibane Renmei, a Japanese anime by Yoshitoshi ABe (distributed in North America by Geneon), and, as you have probably already guessed, the apocalyptic shooter game by Id Software: Doom 3. The first volume is located here:

Haibane Renmei's official (or at least, semi-official) English website is located here

As FHD Remix follows the events of the Doom 3 game, which is known in the story as the First Battle of Mars, Doomguy is replaced by a featherwing being codenamed Tatakai (the Japanese word for "battle") by the mysterious Featherwing Brotherhood. This makes her the Doom 3 equivalent of an angel. Much as the demons are seen to share their properties with humans through hate in the game, featherwings have a much more limited ability to share their wings through love, and the original (still unpublished) Featherwing Love story is the chronicle of such a romance. Tatakai eventually shares her wings with extant game character Jack Campbell, giving him wings with a "mars camo" pattern and beginning an eleven year marriage that ends in the Battle of Armageddon, where the forces of hell take over Earth ... except for a ten kilometre circular area enclosed by a wall inhabited by the remnants of humanity and creatures even more mysterious than featherwings: the haibane ashfeathers Each haibane is named for his or her cocoon dream, what they dreamed about just before emerging, quite possibly the last memory from previous lives. Examples include Rakka (Falling), and Reki (Small Stone). One day, a distraught young lady emerges from a cocoon and, reluctant to describe her horrible cocoon dream, names herself Tatakai...