One day Natsu enters a shop he usually goes to, then he wakes up as a shiba. He thought it was a dream at first but no it wasn't . It was real he didnt know what to do so he went to see the shop owners and all they said is "The only way for you to become human again is to love someone, or else you will be stuck as a shiba forever. But for the 30 first days you can transform back into a human"