Nagato Yuki no Bousou is a doujin novel of Suzimiya Haruhi series, first posted on the eroparo board on 2ch. It's a story from the first-person point of view of Nagato Yuki, tells people why Nagato Yuki's eventual rampage in Suzumiya Haruhi no Shoushitsu.
The work has been translated into simplified Chinese and circulated on the Internet. In late 2006, RB Agency adapted it into a visual novel and published it on the POPGO forums.