14. Even though the show originated as Index, most of its value comes from its spinoff sequel, Railgun. Even so, the two shows are so interrelated, sharing the same cast of characters, that it's impossible to split the two apart. In the end, the name of the series is Index/Railgun, and should be evaluated as such.
Why is Index/Railgun #14? Mostly because of its main character -- Academy City. Not Misaka, not Touma, not Accelerator -- Academy City. This beautiful city is obviously the most cherished part of the author's pen and the artist's labor, you've never seen such a beautiful city. The openings of the anime, in both Index and Railgun, feature these enormous high-rises accompanied by futuristic windmills, robot street cleaners, and super-computer governors. In the vast depths of Academy City, host to millions of people, most with psychic powers that can do any variety of things, you get the sense that anything could happen, that it's a seething underworld of adventure and intrigue. The fact that there are 7 level 5 espers in the city, but only two, Misaka and Accelerator, have yet been revealed, even though we're up to episode 73, shows the vast depth Academy City still has to call upon to surprise and excite us.
Academy City has beings of pure energy and mutant superbabies and psychic tremors. It has whatever the author wants. Guns? Sure. Spells? Sure. Androids? Sure. Vampires? Sure. Mud Golems? Sure. And the trump card to rule them all, a right hand of anti-magic Touma can use to punch through any opponent who comes to disturb the peace. If our future really does look like Academy City, I can't wait to get there.
Index and Railgun are full of ecchi, which tends to weaken the story, not improve it. But the effort they put into making everything look amazing, from the city itself to the characters to their outfits to the magic is welcome, especially in contrast to the half-assed effort of Fairy Tail mentioned just before. Index/Railgun's music is techno and high-pace, just like the high-tech setting and fast-paced plot, they go perfectly together. When Index wants to be cute, it trots out 'Misaka Misaka,' and even when you know you're being manipulated by her girlish looks and mannerisms, you end up swooning over her. When it wants to be serious, in Railgun at least, with the plot of children being sacrificed to an experiment, and the teacher who felt responsible for their murder seeking redemption, the story can make you cry too. And once a story can make you laugh, and cry, and catch your breath with how gorgeous something is, it's really done its job.
Because Index and Railgun aren't really focused on any overarching plot or main character, the story is boundless, as boundless as the creativity of the author, who is still composing more for both series. Even though the second season of Index just ended, I can only hope and pray for a third, or a second season of Railgun, or something! The story hasn't ended at all. It's only just begun.