A news about A Certain Magical Index getting a 3rd season in 2018 had been announced in its official website today. The announcement was accompanied by a new preview which is really fantastic. This announcement simply clear all the speculation as leaks about the 3rd season anime had been posted online few months ago.

A Certain Magical Index Season 3 Preview
A Certain Magical Index Synopsis
Kamijo is a student in Academy City, where people use science to develop supernatural abilities. The guy’s got a lot of heart – luckily for a young nun named Index. She’s on the run from a sorcery society that covets the astonishing 103,000 volumes of magical knowledge stored in her memory. When Index stumbles into Kamijo’s life, she find a faithful friend and protector, and while Kamijo’s easily the weakest kid in Academy City, he’s got something else going for him: the Imagine Breaker, an unexplainable power stored in his right hand that negates the powers of others.
Code name: Yu Alexius is an ambiguous entity who loves to talk about anime and Chinese animation in general. An insatiable soul from the Pearl of the Orient, a frustrated writer and a Houtarou Oreki wanna-be. He is a piece of a lunatic and everything crazy.