To put it out there, Elder/Ancient Primals are just ones that are not being actively prayed to today.
Odin basically tempers a victim to pick up his sword and then uses the host to drain enough aether until he can materialize.
Bahamut is kept alive by ancient Allagan tech.
Belias is a little strangers, as we don't have much lore there. Seeing how he's basically a giant purple/black ifrit-egi, I've seen some speculation that perhaps Belias is an older interpretation of Ifrit that fell out of worship. (If we're assuming primals are the way they are because of how they are believed to look like, this could make sense). Otherwise, Belias simply falls under the category of "no longer worshipped" and was just a flickering memory brought alive through the bunches of SMN stones SMN Quest Rival Guy had. >Also, Ascians.
Odin basically tempers a victim to pick up his sword and then uses the host to drain enough aether until he can materialize.
Bahamut is kept alive by ancient Allagan tech.
Belias is a little strangers, as we don't have much lore there. Seeing how he's basically a giant purple/black ifrit-egi, I've seen some speculation that perhaps Belias is an older interpretation of Ifrit that fell out of worship. (If we're assuming primals are the way they are because of how they are believed to look like, this could make sense). Otherwise, Belias simply falls under the category of "no longer worshipped" and was just a flickering memory brought alive through the bunches of SMN stones SMN Quest Rival Guy had. >Also, Ascians.