Nisio Isin

Koyomi Araragi, a third-year high school student, manages to survive a vampire attack with the help of Meme Oshino, a strange man residing in an abandoned building. Though being saved from vampirism and now a human again, several side effects such as superhuman healing abilities and enhanced vision still remain. Regardless, Araragi tries to live the life of a normal student, with the help of his friend and the class president, Tsubasa Hanekawa. When fellow classmate Hitagi Senjougahara falls (myanimelist.net)

The morning after his high school graduation ceremony, Araragi goes to the bathroom to wash his face but is struck by the sensation that his reflection is watching him. Touching the mirror, Araragii's hand passes straight through and he is sucked into a mysterious world. (themoviedb)

In each episode, Koyomi is presented with a mystery posed by one of the female characters from the story, which he then investigates on his own or helps them solve.

Mild-mannered Koyomi Araragi sticks his neck out for a dying vampiress and ends up tasked with fetching her missing limbs. (366weirdmovies.com)