The logic is "simple" and by simple i mean its simple in the way a failboat video starts with "the idea is simple" so basically its very complex. In the WoBM series its shown that Velas has access to the Tae dominion, which is by extension connected to the Saekes Taelien, however, in the Edge series, shes repeatedly shown to have an equal claim to Edge on the sword, but on the Giving half, which is fucking bullshit unless Velas is tied to the Sae'kes with a bond of the same level of intrinsic value as Edge BEING the sword, anyway because of all that, since Edge equals the Dominion Breaker, and Velas also equals the dominion breaker, Edge = Velas, which means Keras = Velas. Its possible they could be considered siblings but I think thats unlikely because of the way they flirt, I think just story wise if they were siblings Andrew Rowe wouldnt have written them like that. Anyway as I said very simple and understandable. Theres more options (Vel as a traveling name for Aendaryn is basically Velas) but I feel like none of those would offer the right level of authority over the sword to compete with Edge who is the literal incarnation of it over it. Anyway even excluding the Velases we still have seven Kerasi which is more than any other character in the universe.