from Boku Wa Tomodachi Ga Sukunai
Kobato Hasegawa is a vampire. Oh, no, wait. She's not.
She's the younger sister of Kodaka Hasegawa, and an avid fan of Full Metal Necromancer, and as such began to identify herself as Reisys VI Felicity Sumeragi, the reason why she wears gothic clothes. She sees Maria as a rival because Maria is a nun, and she's, well, a "vampire", aside from Maria being too close to her An-chan.
In the light novel, it was stated she has heterochromia. But in the anime, there was an episode (or was that episodes?) where she has 2 blue eyes.
Why I choose her? Because she was voiced by Kana Hanazawa. And a season 2 of Haganai was confirmed! XD