Uther was a being of justice on your world. I am sure it was quite surprising for you to see his fate here, following a leader who embodies what he stood against in life.
I believe you should witness this memory firsthand. Take it to my soul mirror, view the memories within.
Sometimes the hard truths are the most important to witness.
Completion
I hope that this memory helps you to understand Uther's path.
Notes
A few yards away is a Soul Mirror. Interact with it and Afterlives - Bastion plays:
On a dusty, forsworn field, a warhammer drops on the ground as Uther falls to his knees, breathing raspily. He looks up at Arthas, drawing Frostmourne from it's sheath. Uther closes his eyes as Arthas runs him through.
Uther: Light... save my soul.
Elysian Hold comes into view as Devos flies toward it with Uther in hand.
Devos: Uther...
Uther: Where... Where am I?
Devos: Welcome... to Bastion.
On the ground, Uther looks up at Devos from his knees.
Devos: You led a truly selfless life, and for that, you have been chosen.
Uther: Chosen?
Devos: To shed your mortal burdens and join the ranks of the ascended, serving to ferry the souls of the dead unto the Shadowlands.
Uther: I serve the Light. And my work is not done. There is an evil that must be s--
Devos: There is no evil here. The darkness was sealed within the Maw long ago.
Uther: You're wrong. He destroyed my home, murdered my people and my king. He must be punished.
Devos: You are an Aspirant now. You must accept your new purpose, and purge yourself of this desire for vengeance.
Uther: What I desire... is justice.
Devos looks at Uther, who is lost in thought, meditating in a field. Thenios approaches Devos from the rear.
Thenios: Devos, why are you training this soul? It is beneath your station as a Paragon.
Devos: He cannot let go. He continues to demand retribution for his death.
Thenios: And this concerns you? Many souls take eons to ascend.
Devos: Yes, but this one seems... broken, Thenios, unlike any soul I have seen. I have begun to wonder whether he was deemed worthy of Bastion... by mistake.
Thenios: Be careful, Devos. I would not let the Archon hear such a thought. In time, he will forget. Trust our ways. Trust the path.
Some time later.
Uther: Devos... how long must we train?
Devos: Until you are ready to ascend.
Uther: And what is keeping me from ascension?
Devos: Nothing but the memory of your mortal life.
Uther clutches his shirt above his heart.
Uther: How can I forget when I can still feel his blade?
Devos reaches to Uther and moves his shirt, showing a wound above his heart on his chest.
Devos: (GASPS) Your soul... is wounded? Who did this to you?
Tears well up in Uther's eyes.
Uther: He was my student. He betrayed us all.
Devos: Show me.
Devos touches Uther's wound and she sees the moment Arthas ran him through, his soul splitting into two. Devos pulls back her hand in shock.
At Elysian Hold, Devos is pleading her case before the Archon and the Paragons.
Devos: The runes on his blade were unmistakable! This dark agent runs free on a mortal world with the power of the Maw itself in hand! Our realm is imperiled!
Thenios: Impossible! The Maw is inescapable. You must return to the path.
Devos: If he had purged his life, we never would have known of this calamity! The path is flawed!
Archon: Enough! The order of the Shadowlands depends on the execution of our eternal charge. You will abandon this course.
Devos: As you command... my Archon.
Devos walks away, intent in her eyes. She returns to Uther, out in the fields.
Devos: Uther! The time of your ascension has come.
Uther: I... thought I was not ready.
Devos: Do you wish to see him punished?
Uther: I do.
Devos: Then prepare yourself.
Devos grants Uther his wings.
Devos: The moment he falls... we will claim him.
Atop Icecrown Citadel, Arthas lies supine on the ground, looking skyward at Devos, who is reaching down to him.
Arthas: I see... only darkness... before me.
The pattern in Arthas' eyes is reflected in the redness of the Maw. Uther is holding Arthas by his neck.
Devos: Now, cast him into the Maw! Return him to the darkness he served! His eternal suffering awaits.
Uther: He was... my student.
Devos: Remember what he did and take your vengeance.
Uther: Not vengeance. Justice.
Uther releases Arthas, dropping him into the Maw.
On complete:
Thenios says: Devos meant well... meant to right a perceived wrong... but Uther was not ready for the trials of ascension.
Thenios says: Straying from the path as the embodiment of loyalty itself set Devos's course irrevocably towards doubt, violence.
Thenios says: Her hand, Lysonia, quickly joined Uther in following her. As our anima stores waned, their numbers grew.
Thenios says: With Devos gone, Lysonia will surely taker her place leading the Forsworn. I pray we find peace before their campaign starts anew.
Soul Led Astray
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[60] Mysterious Soul Mirror
Patch 9.0.2 (2020-11-17): Added.