There is a character, Inachika Akitani, who dies without appearing outside of flashbacks. He is stated to have lived for five hundred years and had amazing levels of psychic ability, especially precognition, based on a connection to the Akashic Records. He loses those abilities about the time the series begins, with no explaination until the characters and reader find out the the Big Bad's motive for destroying the world is to move back in time - meaning he has already destroyed the future world. -skyfell
...which seems to be the full story until Animus mentions seeing his next life in the far past while dying, and that it would take about 500 years of life to redeem his karma...
In a bit of fridge logic or WMG: Three Great Beasts are named Invisible, Hraesvalgr and Unicorn. Unicorn is obvious, Invisible for dragon doesn't have much sense, and Hraesvalgr is just plain outstandingly strange, even while being a shout-out to an ice giant corpse-eater who transformed into a giant eagle. Ice giant corpse-eating phoenix. Inverted to hell and back. But it is also similar to how word "pink" (rose-colored) is written in many languages, essentially making the trio "invisible pink unicorn", a parody religion and its goddess.
When Anima and Animus were kids, they talked about what they would want to do if they gave up their powers and became normal kids: Anima wanted to play with animals and eat food while Animus wanted to be a scholar. In the future, Animus would create Golems with various eyes (like for reading) and one of the golems would be a voracious reader itself. Meanwhile, Anima had the beast knights and ate almost constantly. Being pseudo-gods didn't really change their personalities at all!
When Anima appears for the first time, she is in the dark shadowy form, and that clearly resembles Animus's final form, except spikes. That resemblance hit me when Animus was shown to have no human body. They have long outlived their bodies in the centuries of their life.