THE NIGHT ITSELF (The name of the Blade #1) by Zoe Mariott
When fifteen year old Mio Yamato furtively sneaks the katana - an ancestral Japanese sword - out of its hiding place in her parent's attic to help liven up her Christmas party costume, she has no idea of the darkness she is about to unleash on modern day London, or the family secrets that she is going to uncover.
The paralysing paranoia that descends on her before she gets to her friend's party is her first clue. The vivid and terrifying visions that nearly get her killed are a pretty good warning too.
The giant nine-tailed cat demon that comes after the sword and tries to rip her throat out? Overkill.
Seconds away from becoming kitty-food, Mio is saved by Shinobu, a mysterious warrior boy. But it's already too late. Mio has ruptured the veil between the mortal realm and the Underworld, and now the gods and monsters of ancient Japan stalk the streets of London, searching for her and the sword.
With the help of her best friend Jack, a fox spirit named Hikaru - and the devoted protection of the betwitchingly familiar Shinobu - Mio attempts to discover the true nature of the sword and its connection to the Yamato family. Because if she doesn't learn how to control the katana's incredible powers, she's in danger of being overwhelmed by them. And if she can't keep the sword safe from the terrible creatures who want it for their own, she'll lose not only her own life... but the love of a lifetime.
Isn't the cover gorgeous? When I found it had to share it with you guys. The synopsis makes me really excited as it has such a manga/anime feel to it. Can't wait for this now.