@petnavis I think he did it with excellia.
The hint was on excellia words : I’m not worthy of Hero + every fibre of my being.
The new sword are the first sword born from the union of holy sword and it’s smith, we can deduce that fact since excellia did not lose even her hair, it mean the materials NEEDs to come from elsewhere .... a material that inherited excellia every being.
Ah also “sisters” do you think he only did it with excellia ? Think again....