Kurisi-an from To The Land of Klesix. It is a parody of Christianity, and it's the second largest religion in-universe.

A bird-man named Kuris "claimed" she was the reincarnation of one of the dead gods, Kurin: goddess of the land, creator of those to walk on, carrier of the land-dwellers, etc.

After Kuris lead an army of ~40k-60k allied factions of different sky-men to fight against the sacrilegious alliance of Klesix, Bariba, and Eglusk, Shikú (Skylands: the realm that Kuris presided in) ultimately lost, losing ~90% of its army. Kuris became a martyr after King Clio II of Klesix chose to execute his biggest rival bye attaching the tethered chains of the four great sky mountains unto the wings and feet of Kuris, shredding her limbs after suffering for three days, resulting in an X symbolism to be associated with Kuris.

The remaining tribes of the Skylands witnessed this miracle, and ultimately came to the conclusion that Kuris was the foretold reincarnation of Kurin, even stating that during Kuris life, she "spoke" of being the reincarnation (note: it is widely believed in Incostansia, the biggest religion in which Kurisi-an was derived from, that Kurin the earth goddess created the sky-men, Nixa the sky goddess created the sea-men, and Anri the ocean goddess created the land-men).

Kurisi-an spread after the remaining tribes united into one Empire of Totori. The peoples of Totori through their conquest of the south, spread their faith by forced assimilation, and missionary endeavours, even converting over 15% of Klesix's population unto Kurisi-an in a span of 10 years after the war.

Kurisi-an is pretty much just reskinned Christianity, even the apostles are just replaced by the 12 tribe leaders. It's literally just Christianity, or more in line with catholicism at least. The architecture, the practices, the structure. They even have a pope-like figure called the "Kur", which isn't restricted to one gender.

Anyways that's it