Kamisama Hajimemashita: Kako-hen  

神様はじめました～過去編～, Kamisama Kiss◎ OVA

While playing in the snow at her shrine one day, Nanami Momozono witnesses her friend-the fox youkai Tomome-falling down with dark markings on his body. Lord Mikage, who had been absent for a long time, appears and puts Tomoe into a magical pocket mirror to prevent him from getting sick. Mikage explains that before he and Tomoe met, the fox was in love with a human woman. He made a deal with a fallen god to become human, but instead of living happily ever after, he became cursed and died. When Mikage found Tomoe, the god erased his memories of his human love as a quick solution. However, something has changed recently that reactivated the curse; Tomoe is now in love with Nanami. Since there's no way to stop the curse, Nanami wants to go back in time to prevent it from happening in the first place, even if it means she may never meet Tomoe again. As she travels through hundreds of years to save her beloved friend, Nanami discovers that their bond is much stronger than she ever imagined.