The Claire seen in the Moon That Never Sets is the younger version of Haschel's daughter and Dart's mother. She switches between a state possessed by the War God and an innocent state of her own consciousness.
The player must fight her with Haschel on the Moon That Never Sets. At her current youthful state she doesn't recognize her own son Dart as stated by Haschel before he goes to meet her in combat.
Haschel's long lost daughter who disappeared after accidentally killing her best friend during combat training in frustrated response to Haschel's harsh words. She later in life met Zieg, Rose's former lover, and married him. When the Black Monster came to Neet looking for the Moon Child, Claire went back to help the other villagers alongside Zieg, but perished.
Claire is a challenging boss, but not too difficult. She has one special attack, Four Gods Destruction. Her first set of attacks are a simple set of physical attacks. After about 3/5 through the battle, she uses her special. This attack will reduce Haschel only to 1 each time. She uses this once or twice then continues with the physical attacks, but from here she does two or three attacks in a row, so after the round of special, use blocks to heal yourself.
Though it is not stated directly in the game that this Claire is both Haschel's daughter as well as Dart's mother, it is made painfully obvious when Haschel discovers Dart knew the same tune as his daughter, who had said she would teach it to her child one day. This is reinforced by Haschel's comment: "...She does not know you yet", implying he knows of the connection while Dart remains oblivious.