Fox Dens are plentiful on the map in Ghost of Tsushima, and each of them will take you to an Inari Shrine that you can honor. This action will have a beneficial effect as for the hot springs. The reward will be different according to the number of sanctuaries already found. Initially, these shrines will increase the number of minor charm slots in your inventory. Note that they are incompatible with the major charms obtained in Shinto Shrines.
Once the 6 locations of minor charms are unlocked, you will get 2 special minor charms by continuing to honor shrines. And, finally, keeping honoring shrines will increase the power of these charms.