What to do with Lewyn?

I wouldn't give special spiral to L!Ike tbh, he already has tremendous special CD on enemy phase. Heroes that make effective use of special spiral are ones that can drop large aoe bombs through skills like blazing wind, though there are other niche uses for it too, usually dependent on the prf weapon.

Celica, Ophelia and Owain are all good users in addition to Lewyn.

But yes, a -Spd Lewyn is probably not going to do great. But probably just hold onto him if you don't have any of the guys above.

If you already have built green mages, then you might as well fodder him (especially since the IVs you have aren’t exactly ideal)

34 + 4 from A slot +6 from buffs + 3 from weapon =47 maxish potential

Think about what you would use him for. I got a -attack and a -speed, both of which hurt. I am still on the edge if i want to use either one. He is still usable with bad IVs but I gotta think about merge potential and max effectiveness.

My goal is for him to replace Nino in my Aether Raid defense, Which he may struggle to do with those ivs and low/no merge.

Definitely keep him. He is still extremely fast. The only key doubles you miss are units like Ayra, Ryoma, Mia. You still double units like SY!Tiki and might get the kill on her. You don't care about Spd against blues and a lot of greens because he can one shot them with his special charged anyway.