What exactly is fate ?

Seh said his fate was war to die in an accident, but now he says his fate is something different and he doesn't know it yet.

What exactly is fate ? Is this some kind of ability like OHS's ability? Whatever that true manipulation was ? If yes then isn't his power looping ?

For god sake they Literally make him immortal bum by saying he doesn't have any talents as an immortal because he doesn't know his fate.

Is there any difference between fate or normal people and ender's ?

So the head realm is the gate to go back to their world ? That whole realm is kinda sus.