I've suspected for a while Kotoyuki was a creep who had an obsessive crush on Hinako after she saved him from the fox and years later used his family's money to basically buy her in marriage by paying off her father's debt. The evidence is mounting

Maybe one reading for this ending is Hinako represents young people rejecting old traditions like arranged fox god marriages and leaving the rural villages. The process ends with the villages empty, the traditions forgotten (sped up by toxic gas)