Core Guardian
For Rhode, this information wasn't difficult to understand. It explained that the summoned spirit consisted of both Light and Wind element which meant that this would increase its resistance against those elements. However, this wasn't a common occurrence. The Spirit Bird was a Wind elemental creature which had no relations to the Light. It was like a Microtus having a family with an eagle.
The only possible reason that he could think of was, during the process of evolving, the spirit got affected by external elements. If those elements were strong enough, it could be enough to input certain new elemental attributes to it.
However, Rhode couldn't accept this as an answer. Instead, he became further confused.