After defeating Vermiform Edward, return to Halgita and bring Eugene to see Karin, an aristo on the third floor. She will tell him to find a ring that Svala lost. Speak to a guard by Svala's quarters. She will say that animals entered the room and caused trouble. Have Rico speak to Shibuff, old dog on the sub-floor level where the shops are. He will tell you that a mouse has the ring. Bring Rico to the second floor where the mouse David, lover of shiny things is in a room. He gives you the crested ring. Bring Eugene back to Karin. Finally, return to Svala to receive the Casandra ring.