You do realize you can purchase your base relic from the calamity vendor in Gridania and then spend the 900 myth to upgrade it to a Zenith?
Most likely, yes. But with all the myths you need already for animus, why would you want to waste even more of them on something like that?

Been keeping my bow in zenith form simply to farm atma with, even though it's a weapon I would like to upgrade :/