Celsius was a minor villain in Tales of Xillia. She was a spirit that acted as Gilland's assistant. When King Nachtigal was defeated, Celsius was ordered to assassinate him with large icicles. Later on, she and Gilland fought Jude's group together.
In Tales of Xillia 2, after Gilland's death, Celsius had been resting inside her spyrite until she was awakened at the Research lab and ran off. Throughout Jude's sidestory, Jude, Milla, and Ludger often tried to convince her that they never meant harm. After their first fight, Celsius requested that to prove themselves by visiting Kijara Seafalls, Fennmont, and Fort Galdala. It was revealed in the past that she and Professor Haus visited those places together as well. At Fort Galdala, she summons a seadragon and fights Jude, Milla, and Ludger again. At the end of the sidestory, Celsius went back inside her spyrite and became Jude's to use.