Toaru Majutsu no Index SS: Biohacker Arc (とある魔術の禁書目録SS -バイオハッカー編-?) is a side-story which is to be released in parts with limited edition DVDs and Blu-rays for the Toaru Kagaku no Accelerator anime.
Welcome, Kamijou Touma-kun, to the colorful underground!
Kamijou Touma meets two girls in Academy City's back alleys. One is Mitsuari Ayu, a lady of Tokiwadai Middle School with the Mental Stinger power to control people's minds. The other is Kumokawa Seria, a mysterious genius high school girl who can control people's minds without any power.
Kamijou is at the mercy of those girls, but those peaceful times do not last long. That kind time is torn apart by a gigantic creature that towers over them: a dragon. Who is the Biohacker who created it, controls it, and freely gives it the power to fight?
Why is that giant creature pursuing Mitsuari Ayu? Kamijou Touma enters Academy City's deep darkness to protect the girls.
It all happened one year ago. It is the summer of Kamijou Touma's third year of middle school. This is an untold story different from the time he spent with Shokuhou Misaki. Kamijou Touma's starting point begins here.