[quote=@Zeroth]
From here on out, as we begin to explore the world, how much control do the players have over the story? Will any beasts we encounter and fight be treated similarly to players, going back-and-forth with the GMs until one side dies, or will that be reserved for "boss" monsters while lower ranked creatures can pretty much be auto-hit/killed as long as it's not excessive (like if someone writes about tearing apart over a hundred fodder creatures in one go)?

Will there be any kind of bestiary to be filled as we go along? And as for the "NPCs," so to speak, of the town or other locations in the world, how will interaction with them play out?
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Pretty much what you just said. As long as you make it reasonable when you kill those hundred fodder monsters. For example, I don't expect Kenji right now to fight off at the most one monster, maybe two. But if Kenji gets stronger...

Furthermore, all monsters are controlled and introduced by the GMs.

A bestiary will be filled but it must be obtained on a certain quest first that is unavailable at the moment. As for NPCs, all of them are controlled by the GMs. Mostly me.