Somehow, the runes of the enchantments woven in the fabric were capable of channeling Raagu's mana.
She had no need to manifest any rune that was already present on her mage robe, she just had to circulate the proper elemental energy and the artifact would do the rest. Conjuring runes was akin to writing words using mana as ink.
The robe, in turn, acted as a printer with a pre-set series of characters that needed mana to be traced with mechanical perfection.
Much to Lith's dismay, that was all he could get since the cloaking spells of the artifact hindered the Eyes and he had more important things to do. The Throndar wasn't afraid of the puny humans and wanted to teach them a lesson for invading his turf.
The gleaming metal of the Wayfinder and the powerful white crystal would be a fine addition to his resources, maybe even enough to craft proper armor for his massive body.