Inuki

Inuki is a god-dog given to Yuzuriha Nekoi when she was a kid. He is her best friend and companion. Inuki can transform himself into several thing including the shape of a sword where he helps Yuzuriha fighting. He can't be seen by ordinary people, and this made Yuzuriha really sad when she was young - people used to call her a lier for her telling that he was at her side, and nobody saw him.