Riftmages of Phylos
One cannot be a riftmage without first crafting your own Athame, a tool for opening and closing rifts. It is chiseled out of astral ore and bound with a soul. Usually a dagger or shortsword, but an Athame could potentially be any bladed weapon. The soul energy contained is still a shadow of it’s old self and can lend it’s abilities to you.
In games terms, an Athame will always be starting at a +1 Enhancement Bonus, but later more powerful ones can be acquired. There will also be another enhancement bonus in the form of an effect (flaming, keen, etc.). This can be exchanged for the ability to cast a low level spell an appropriate number of times per day.
A warrior priest of Selsha is noticed by a master and invited to train under him. For the creation of his Athame, a crystalline astral ore bastard sword, he captures the soul energy of a fire elemental. His Athame could conceivably be either a +1 flaming bastard sword or a +1 bastard sword that can cast Burning Hands once a day as a wizard’s arcane bond.