[Flere821]

Originally Posted by Darial

Just to add on to the excellent summary by Flere821. A little more spoilers on Eugeo:

Spoiler:

However, even after dying and taking off with child Alice, the spirit of Eugeo still made two appearances (that I remember) further down the road.

First to add his strength to wake up Kirito from a coma for the final fight in the Alicization arc. He also materialized briefly at the very end of the Alicization arc when Kirito & crew returned to Underworld again. So it seems like a part of Eugeo is sticking around with Kirito via his sword.

Some clarification:

Spoiler for Eugeo:

Those appearances from Eugeo aren't from his main Fluctlight, that was explicitly stated to be deleted. Those parts are from Eugeo's partial fluctlight that's left in the Blue Rose sword, all the times he used 'Release Recollection' left a imprint of his soul in his sword.