Light novel written by Fuyuki Shinobu (冬樹忍) and illustrated by [[Sakusaku]].
Title: 二次元の砦を守るには不本意ながら彼女が必要らしい
Official website: http://hobbyjapan.co.jp/hjbunko/2jigen/
nijigen no toride wo mamoru ni wa fuhon'inagara kanojo ga hitsuyourashii