I read it originally with kindle (amazon book). It is a book about two main characters, one female and the other a male - I believe it is a young adult book, Sci-Fi, paranormal, romance and magic.
So on with the details:
The male, I am fairly certain, is some kind of demon who has "pet" like dragon and was paired with him at birth I think more like a familiar/pet. So he has to steal a jewel to free his sister.
There is like a demon realm and the human realm and in the human realm there are "safe heavens". They are managed by Sorcerers? I think and the jewel he has to steal is highly coveted and being held in one of these safe heavens in a vault until this magic counsel decides what to do with it. So he goes there with his friend whom I believe is a incubus or succubus?
This safe heaven in specific is run by one man that has a twin brother and a daughter - anyways basically the jewel was to be stored in a protected room in the safe heaven but her father who runs it gave it to her in secret - the little pet of the demon guy steals it from her and takes it back to his owner the demon guy.... It's actually rather funny how it happens because she's chasing the thing down the hall and to this guys room.
He gives her a fake one (unbeknownst to her) - there is an explosion downstairs where the vault is, she runs down there and believes her father is injured, they (her, the demon guy with the pet dragon and the succubus) all get attacked by another demon and they have to run for their lives..
Eventually they cross realms because they are being hunted for this jewel/stone...
If this rings a bell with anyone I really want to find the book series I think there are 3-4 books in the series?