Also known Kizumonogatari. The story were Koyomi Araragi first meet Shinobu at her original form as a beautiful vampire who had lived for more than 500 years, and the cause how did Araragi got involve in the supernatural world and almost turn into a Vampire.
At last the prequel of the Bakemogatari is going to be an Anime. Now will know how did unlucky Araragi got himself attack by Shinobu and turn into a lucky semi-vampire Araragi.
If you think of it, If Araragi have not meet Shinobu, He won't able to help all the girls that got involve in the supernatural. Even he do help, I bet he be die already at the first Tsubasa Cat problem.
"Losing strength..., Too soft!!"
In other words Shinobu was the Key character that made the main protagonist who he is now.
Here a PV of Kizumonogatari