A god's duty seems to be a part of a god's (ie Kanaruzawa) daily life. For instance, Sekai has to regularly enter a dark room (seemingly hidden underground after a set of iron doors) where hands come from "void" to catch her. This duty seems rather unpleasant to be done. It also seem quite mandatory (why would gods bother themselves in doing something so nasty if they could easily avoid it).

God-s duty