User blog comment:KKytes/Dark Vortex Arena/@comment-33953722-20180104162528/@comment-26140304-20180104194205

It's achievable, but it's a bit of a stretch considering Kikuri is the only Dark OE who has BC cost reduction on LS. Hers is only 20%, which is underwhelming compared to the 25% and 30% leads we've recently been geptting, such as Bjorn, Cerise, Ezra, etc, but it gets the job done.

Even then, it's still quite a stretch considering Neferet and Velma are the only dark units with 25% passive BC cost down, be it on SP or ES. The only way you'd be able to achieve 0 BC cost would be using Ortus and Elder Hat. There's Ragnarok Edict, but I only imagine very, very, very few players have it. Going back to my earlier example, Velma would probably appreciate 0 BC cost more than Neferet, considering Velma can inflict status ailments, which aren't protected by the opponent's side unless units have passive status negation on their spheres or SP. Extra Skills are disabled for opponents, including Elgifs.