I believe so, and I think the event is triggered randomly. For my case, I noticed the event when I heard a roar while traveling between maps. The rabbit always appear in the darkwood. As for the drops, Bianca can use pickpocket to get "Claw of the black rabbit" during the battle. However, there seems to be a bug: After defeating the rabbit, MC will say he got an interesting trinket (Black rabbit foot accessory, according to a reply to my inquiry few posts above), but this item never appears in the inventory.
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