|Oh, and she's also voiced by Kugimiya Rie|
At their first meeting, our Main Character will learn that the Girl is involved in some manner of fantastic occurrence. Circumstances will reveal that the Main Character is now also tied to the abnormal events, forcing him and the Girl to live in close proximity. Despite their initial inability to get along, the two will overcome their circumstances and eventually admit love for each other.
As one may have guessed from the title, I am describing Aria the Scarlet Ammo. I am also describing Shakugan no Shana, Zero no Tsukaima, To aru Majutsu no Index, Lotte no Omocha, and to a lesser extent Hayate the Combat Butler and Toradora!. There are likely many more anime that utilize this formula, as well as countless light novels and manga who are aiming to be the next smash-hit by using the same successful formula.
Actually, that assessment may not be completely right. Maybe it would be better to include Aria the Scarlet Ammo in that final category...