[quote=@Mae]
[@ZAVAZggg] someone who wanted to enchant weapons or create spiritually bonded weapons would be a-ok as well.

<Snipped quote by RainyHigh>

ahahaha, this is even more perfect. Someone took the last baked good? Thanos'd. Someone gave you a weird look in the street? Thanos'd. 
[/quote]

What if someone bonded on a spiritual level with a demon, think symbiotic possession, and then used a soul stealing blade in order to bolster the demon's magic as well as maintain their mutually beneficial relationship without incurring damage to their actual soul?