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One thing that stood out to me in the lore video was the giant snake that appears to be shedding it's skin. Hotaru and Hestia are scared by it, and Peke who's a former goddess seems to know something about it and is informing the hero Nagi about it. The snake must have some meaning because it's the only new living thing introduced in the animation besides Hotaru's mascot. If Nagi has been isekaied as the hero, and has essentially formed a party with the other girls there's probably a demonlord or big boss they're supposed to defeat. I think the fifth member will either be the demonlord or the final party member they pick up to defeat them.
