Kokkuri claims that, when he was young, he was worshipped as a god at his shrine. He claims that he was needed, but as times progressed, the common people that once believed in him began to fade. After the shrine was demolished, he also lost his home. Kokkuri has already known Kohina from before he started to haunt her. As Kohina was the only one to often visit the shrine that remained for him, even in its ruined state.
In the manga, Kokkuri-san is shown to have met Kohina in her past life. Wherein Kokkuri-san was wounded and Kohina planned to take him in, nurse him, and feed him so that she would eventually eat him. However, Kokkuri-san showed Kohina that he was a fox spirit and she lost interest in eating him. Kokkuri-san stayed with Kohina and found at that she stayed by herself because she didn't want anyone to be sad when she died from her illness. This made Kokkuri-san very sad (he said so himself). On the day that Kohina was dying, he was crying so hard and tells Kohina that he hasn't yet repaid his debt to her. Kohina says to not bother anymore for she will not smile. Then Kokkuri-san says that he will follow Kohina even in her next life and promises her that he will make her smile everyday. Kohina looked surprised and smiled while she made a promise to Kokkuri-san. He did not see Kohina smile because he couldn't see through his tears.
In the first episode of the anime, Kokkuri-san says that he has a promise to fulfill to Kohina and that was the promise he made with the Kohina of the past.