The Sword of the Creator requires a Crest of Flames, with crest stone (canon Byleth, checks out). Aymr: Seiros Areadbhar: Blaiddyd Failnaught: Riegan

So, in SSBU, Byleth must have the Crests of: Flames, Seiros, Blaiddyd, and Riegan FOUR crests. FOUR.

Sakurai… What have you created?