To have pushed so and hard distroyed so much for sword logic, he realised that existing after defeat would make him the ultimate hypocrite.
He was, after all, a being of principals, and unfortunately they got him killed in the first place.
It was a bittersweet ending.
The line "atleast the stars will remember the shape i gave them", is probably the best line the franchise has ever delivered.
Whether right or wrong, there will always be an indicator that he existed and maybe that's enough for anyone, regardless of who they are.
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I wish could have killed all big three. Sure we kill the Echo of Oryx, so there goes big bad number one, ending his existential crisis. I would have liked a Kingsfall-ish fight to end Xivu Arath once and for all. I also would have loved to kill Savvy and then grab little Immaru and squash him like a bug. I guess in the end none of the big three truly followed the sword logic, so it is what it is, kinda boring and not as big of a fight as I was hoping for. Like let me take Willbreaker and end all this once and for all in a true showdown.