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Apparently, Uller was incapable of channeling the power of Chaos from the Fragments of Ragnarök for some reason. Could this be dependent on his own affinity with this element? After all he's still a soul of his own and all. The sole reason he got the power of Darkness must be that it was a latent Affinity he had for the element itself.
Then what about Benladann's weapon? I do remember I made her an Ice Axe which I've constantly repaired and enhanced every time I could, almost each time I evolved I used my new set of scales to enhance her axe. I had also used a fragment of my soul to make it a "Living Weapon" that could grow stronger by itself similarly to Skadi and Uller, but the Axe itself never spoke to me, so I had no idea what's her personality even.
Check "The Protagnist's Sister Is Actually the Strongest"!