Comments on Krelian's will, purposes and final destiny
At the end of the game, Krelian chose to follow god and walk the "Path of Sephiroth". However, when he says that there is no more a god who could forgive him, and that only god could do such thing, it is implied that Krelian is god itself, or is just about to become god. The Zohar and Deus System had been destroyed, the Wave Existence could return to it's dimension, and Krelian supposedly occupied the "new place" left.
Although Krelian is still a human, he finally ended as one with god, becoming an entity even he did not believe could be capable of existence.
As for Fei and Elly, the reincarnations cycle ended and no more sacrifice would be needed, since Krelian is now the major entity, and apparently would not seek to "reconstruct" himself with human parts.
In the end, Krelian worked as a "tool" for the Wave Existence, paving the way for it's return to the outer dimension. This is something Fei and Elly realized before, but Krelian would not understand it until Deus and Zohar were destroyed.
Krelian received god's forgiveness because his actions were drove by one purpose alone: his love for Sophia.
Krelian never understood his true feelings and intentions, but the answers for all the questions he wants Fei to solve, before the final confrontation with Urobolos, are within Krelian himself.
Krelian was created as an image and resemblance of god. And for this, he acted as he did.