<p>Well in mythology, Yama/Enma is some kind of 'judge' for recently deceased souls, examining the good and evil deeds in life and then deciding what will happen to the soul accordingly (hell, pure land, rebirth...) So it would also be possible that every soul has to face him at some point, meaning the recently deceased villagers were still in his domain, whereas jiraiya was already in pure land... Also Sakumo seemed to still have unresolved 'attachments', making it impossible for him to 'pass on' (into pure land), so he too was still in an in-between stage somewhere around Yama's realm.
For the actual apparition used by Naraka path, i personally consider him a being of the same level as the Shiki Fujin reaper, something that is not entirely a jutsu (phenomena based on chakra and therefore man-made) but has some kind of own transcendental reality (they actually ARE some kinds of 'real' demons/deities)
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