Muelina's research into the Divine Fortress was frustrated by the Defenders of the Eye of Reshanta. Not knowing what purpose the Defenders serve, she doesn't dare destroy them all, but she asked you to gather cores from a Aether's Defender, Fire's Defender, Ancient Defender, and Nature's Defender for her. You defeated the Defenders lurking in the lower levels of the fortress and returned with four different types of cores as Muelina instructed. She will send them to Grunn, an expert in the denizens of the Abyss.