So many worlds of cookie cutter fantasies, for those who are summoned or died and reincarnated.

This story actually follows thirteen different worlds, each with a different "MC".
Six these worlds are reincarnation worlds, while the other seven are summoned worlds.
Each world follows a different trope, and every possible type of story for each world. The Reincarnates either reincarnate as farmers, nobles, or monsters, and the Summoneds either come with their class, separated from their class, or are betrayed by a classmate or two.

Now what brings all these worlds together? A warlord from WeirdSide has set his eyes on them, and sends his army of warmongers to tear them down, and loot the planets of all their resources, and any magical artifacts.

The story follows two primary Mcs. A noble reincarnate, and a mercenary from WeirdSide who deicdes to train a class of summons for the upcoming war.
Even though a huge army of technology advanced invaders are ripping the worlds apart, many factions, both human and demon, can't seem to put their differences aside against a common enemy.

As for harems, expect fourteen.

Note: the WeirdSider mc has already married his harem at the start of this novel.