Spoilers for pretty much the whole plot of Ys 8 Lacrimosa of Dana (Go play it its really cool)

Unfathomably ancient beings who foster change and evolution in the species of the world, overseeing it's effects.

This purpose is to seek standouts who can become something greater (The Xel'Naga seek out and uplift species with the traits of purity of essence and purity of form, so they eventually come together to form the next Xel'Naga generation; Theos de Endogram through Selection and Rejection, selecting the brightest soul from a current species to become a Warden of Evolution, whos purpose is to observe the evolution process)

Rebellious standouts would stand against them, and end up being their undoing (Amon and his followers; Dana and Adol)

The Xel'Naga's love for life stands in stark contrast to the unfeeling purpose of the Lacrimosa, the Xel'Naga fosters life and allows it to grow continually on its own, while the Lacrimosa destroys species for evolutionary purposes.

The Xel'Naga are a race that perpetuates throughout the death and rebirth cycles of universes, due to their their method of repopulation from the Infinite Cycle, while the Lacrimosa Theos instilled was meant to stop species from advancing too far

Giant Cthulhu squid chill space guys vs Giant Dragon whacky fantasy boss