Recource Mangement

I feel that way about aether on a lot of units. Like, Brave Hector? Every time I saw him in arena with aether I thought "thanks for the free kill"

Ok, this is a slightly different matter. You actually have somewhat of a solid case here, and if I say otherwise I'm a hypocrite because I basically recommended this exact idea to ZekeMyHero in his question (which is still on the front page as I write). Just to clarify what I mean:

Ayra's blade
(Reposition, or whatever assist you choose)
Aether
Distant counter
Special spiral
Atk smoke
Spd smoke or something else, say, distant def

It also works with slaying edge+spd, but that looks to me like you're just giving up 2 atk for no reason.

The design of the build is that aether is at 3CD or less at the end of a battle. One hit from Ayra plus one hit from an attacker equals three charges, so aether will activate unless she initiates against an opponent that can't counter, in which case she might not need to heal up anyways. My experience is that this kind of setup sustains quite well in PvE. I've gotten out of situations where I thought for sure I was losing my tank.

The main weaknesses of the build that I can think of:
- her res is kind of weak. But with 25 at +10 and distant def, 31 and stacking attack smoke on it, she might actually be fine.
- HP pool is a bit thin for a sustain build if she doesn't have summoner support. Probably not decisive when she has 35 def.
- atk stat is maybe a little low for aether sustain targeting def? compared to Soleil, for example. Her statline was designed with Regnal Astra in mind. But her atk isn't exactly low either. I think it's definitely workable.
- aether won't activate during her first engagement. Can probably get around this issue by starting with a bait and then unleashing aether against a fresh opponent on her turn.
- you are super-screwed against breakers, but if that wasn't the case what are breakers for? The only way around this that I know of is to tank as hard as Roy or to be a manakete and pray that L.Marth doesn't appear

The other criticisms I would have of the special spiral strategy are in comparison to other options.
- It's probably better done on Eirika, who can stack +12 on all her stats by double-dipping tactics and have 42/44 defenses at +10 while still having like 50 spd and being infantry.
- Ayra is more dangerous with slaying edge+spd, wrath, and Regnal Astra because she can activate it twice in the same engagement. It does cost your sustain, though, which definitely matters in PvE, and using wrath when a healer is involved can be tricky.

The last thing I would say is that if you can gather 100 orbs, I calculated for you a 57% chance of obtaining Lewyn again. The GamePress "should you pull" seems to confirm my theory-based calculation with data they crunched from their simulator. We have this banner for another 10-11 days which is a third of a month, which means 100 orbs might be doable.

So for sure, hang on to him at least until you're done with TT, and as we near Sept 20 you can decide whether you want to try to pull him again and whether you would fodder your only Lewyn, with an amazing IV to boot, for aether Ayra.