Panic-At-The-Impala
AU of seventh year. Crookshanks was Lily's familiar, and became a Horcrux, rather than Harry. Harry is still a Parselmouth, but he doesn't hunt Horcruxes with Dumbledore. Dumbledore is not dead, and neither is Sirius. Tonks and Remus never got together, rather Sirius and Remus got together. Dumbledore found and destroyed all of the Horcruxes, including Crookshanks. Harry lives with the Dursley's until his seventeenth birthday, when Sirius comes to take him to Grimmauld Place. Harry has yet to defeat Voldemort, but he plans to take him on within the next few years.
A familiar is an animal that is soulbound to a witch or wizard. Crookshanks was bound to Lily, which means he would die for her. It also means that he was there for her when she needed him. After about six weeks, their magic synced, and they became a lot closer. Eventually, after maybe ten or so years they could have been able to speak to each other through their minds, but she was killed before they could progress that far.
In this story, we follow Harry as he finds his familiar, and his journey through life as the only Hogwarts student since the Founders to have a familiar in the castle.