How many Millennium Items are there in the original Yu-Gi-Oh! story?

How to get close to this number

Seven again, and for the same reason it appears everywhere else in fiction: it is the canonical count for a set of mystical objects, inherited from folklore and religion. If a story involves ancient artefacts with individual powers scattered across the world, seven is the default answer before you know anything about the work.

The Egyptian framing reinforces it rather than complicating it. Mystical numbering in stories drawing on ancient Egypt tends to follow the same conventions as European folklore does, because the convention comes from the storytelling tradition rather than from the culture being depicted. The number is a narrative choice dressed as archaeology.

As with the Dragon Balls question on this site, the count is fixed because the objects are the plot. A collection quest needs a known target number or the audience cannot track progress, so these counts are unusually stable across adaptations — unlike character rosters or episode-level details, which drift freely between manga and anime.