Bloody Wolf's Darkness Blue: Fist of the North Star Rei Side Story (蒼黒の餓狼 -北斗の拳 レイ外伝-, Sōkoku no Garō Hokuto no Ken Rei Gaiden) is a manga series by Yasuyuki Nekoi. It was originally comprised of two one-shot stories published in the March 22 and December 8, 2006 issues of Weekly Comic Bunch. This version of the manga was entitled The Magnificent Avenger (華麗なる復讐者, Kareinaru Fukushūsha). It was later picked up as an ongoing series for Weekly Comic Bunch, running from April 2007 – July 2009 and spanning six tankōbon volumes. The series was originally subtitled The Hungry Wolf Saga (餓狼編, Garō Hen), before receiving its current title.
This story is a spinoff prequel to the original Fist of the North Star by Buronson and Tetsuo Hara, and covers the events of Rei's life prior to his appearance in the manga. This includes how he became successor of Nanto Suichō Ken and his history with characters both old and new.