Toaru Kagaku no Dark Matter Story
The tenth manga series based off of Toaru Majutsu no Index. An original side story written by Kamachi Kazuma and illustrated by Kisaragi Nankyoku, it focuses on the past of the Level 5 Kakine Teitoku.
This is the best place to read Toaru Kagaku no Dark Matter online.
And here are the reasons why.
Q: Is this the official site for Toaru Kagaku no Dark Matter?
A: No, The entire site is fan-made.