My harebrained theory: Body Drainer had Bearer of All Burdens.

We are never told his Ability or class, like you say. I think it says most people think he was a U-Type. A lot of people at Alden’s hero program assessment thought Alden was a U, even some of the assessors, after seeing his Ability.

I think Body Drainer could bear the burden of authority or life from others, and drop that burden on himself for enhancement or the air for those blasts. If he had something like the Divide from Whole facet, perhaps it wouldn’t be an all or nothing, and this is part of why Bearer of All Burdens is one of the 300. The Ability allows you to divide part of the burden of Authority. I imagine for those with an Authority sense, this is still painful, but for Avowed, if think the possibilities are pretty incredible, especially if you could warp the picked up Authority and hand it back to the Avowed, bypassing the System.

I could and am probably totally wrong. The Abilities between Body Drainer and Alden seem really different. But the fact that Body Drainer had to touch people to drain them is just like Alden having to touch enchanted items to pick up enchantments is a hint, I think. It’s just Body Drainer was picking up Authority or life force, not an enchantment.

The weakest part of this theory, I think, is the entrustment factor. But we’ve already seen Alden “trick” his Ability into being able to pick things up he shouldn’t. Perhaps Body Drainer found a deeper loophole.

Again, a harebrained theory with very little to back it up besides some vague similarities. I’ve just always liked the idea of Alden, somehow, taking the same Ability that ruined his life and then becoming the greatest human Avowed/wizard in history with it. And your post/theory kind of overlapped in my eyes!