Celine has a shy mysterious personality. Being an animal, she has many cat-like traits and can act very distant at times.Like most cats, she is not fond of dogs and she can also speak the human language.
Celine is also a bit of a tsundere as she can be cold and harsh, yet also shows a warm side to people like Emma, Elise Schwarzer and Princess Alfin Reise Arnor. She also often encourages others to find their own answers. However, she does sometime admits that there are certain mysteries of which even she is not aware of the answer to. She also does not seem to be fond of the Septian Church, possibly due to witches having been prosecuted by them at one point in time.
Celine shows a great deal of dislike towards Vita Clotilde and her familiar Granios because of her betrayal of Hexen Clan law.
Celine is a black cat who serves as Emma's familiar and guide to the world of magic. She has been informed about a great deal of things related to magic from Emma's grandmother (e.g. Spirit Shrines) and knows a great deal of magic herself. While pretending to be a normal cat, Celine serves as one of the Overseers for Rean Schwarzer's Awakener Trials in Trails of Cold Steel I.
In Trails of Cold Steel 1, Celine is first seen lurking around the Old Schoolhouse building as well as at several other places around Trista. She appears to be an ordinary cat at first until Rean almost catches her talking to Emma one time. Emma though just tells Rean that Celine is a cat that she had smuggled in.
First Awakener Trial
After this encounter, Celine begins acts even more mysterious and begins to pull suspicious stunts. One such stunt is when Celine lures Elise Schwarzer to the chamber where the first guardian is located in the Old Schoolhouse. She then watches on as the Guardian begins to attack Rean and watches the awakening of his Oni powers. When the rest of Class VII come down to help Rean, Emma notices Celine and glares at her in anger.
When Rean's group goes to Legram for a field study, Celine is seen secretly boarding their train. Later that night, Celine has a secret conversation with Emma. In the conversation, Celine notes Victor S. Arseid's perceptiveness, but states that he probably won't notice her midnight stroll. She then expresses doubts about the reliability of Rean's combat skills, to which Emma tells her that it's not for them to decide.
Emma then sternly reminds Celine about their role as Overseers and that their job is only to watch and guide Rean - not to jump to conclusions or pull stupid stunts in order to force his progress. Emma then warns Celine to never pull what she did again, as they are only meant to be Overseers and that her actions could've gotten Elise killed. Celine shakes it off though and warns Emma about a mysterious power within the Saint's Castle.
Celine then watches over the group from a safe distance as they explore Lohengrin Castle to find some missing boys. She then follows the group to Garrelia Fortress and resumes her role as Overseer for the rest of the game.
Discovering Valimar and the Invasion of Trista
During the preparations for the school festival, Celine and Emma escort Rean and Class VII to where the last trial awaits them. After Valimar is discovered, Celine continues to wait until Vita Clotilde reveals herself during the assassination attempt on Giliath Osborne.
During the Invasion of Trista, Celine reveals herself and her ability to talk in front of Class VII and helps Rean activate Valimar for the first time. After Valimar is badly damaged during Rean's fight with Crow Armbrust, Celine commands Valimar to withdraw despite Rean's outbursts of his desire to stay with his classmates. Celine then watches over Valimar and Rean until they fully recover.
In Trails of Cold Steel II, Celine is first seen when Rean wakes up in the Eisengard Range. She informs Rean on what has happened and of his status as a Awakener. She then informs Rean that Valimar still needs to charge as he used all of his energy to heal Rean. As the two of them walk down the mountain to reach Ymir, Celine tries to talk to Rean several times, though Rean just mostly ignores her because he is more concerned about his friends' safety. Lashing out at him, Rean apologizes to Celine for his behavior.
When Rean becomes aware that Celine had purposely lured Elise to the guardian, Rean gets angry and scolds Celine. Celine though brushes it off by saying that the Guardian wouldn't have attacked Elise as its been pre-programmed to attack only the Awakener candidate, earning another angry glare from Rean. Seeing his face, Celine also admits that she felt bad about what happened and apologizes to Rean.