Find the "Rabbit"

Journal
''A child in Castle Atos pulled me into a game of fox-and-rabbit. I'm the "fox" and have to hunt down the last rabbit left in the game. The "rabbit" is actually a child wearing a lepus mask hiding somewhere in Castle Atos. If I find the rabbit today, I'll collect their rabbit's foot charm and bring it back to their "huntmaster". But if I am too slow, I lose and can try playing again tomorrow.''
 * The following information below is not verified or confirmed and may not be accurate.