This shrine holds the god who kept Tensashihikoinochi company when he came to came to Nibu—a land deity who was originally from this island.
To this day, there are many shrines on Chiburijima, but in the past, there were even more shrines. When there is a small shrine next to a larger one, it usually signifies the two were combined. This sort of combination is likely a result of one of these shrines being originally located atop some mountain and becoming too difficult to manage.
By the way, this is the shrine with the most stone steps in all of Chiburijima.