claude knows abt the black magic and hes aware of the first prince having black magic bcs he saw his brother space out into something that looks black. He's protecting athy from the black magic, the nobles and to ppl who wants to hurt her bcs he stole the throne from his brother and he knows that some nobles might use athy as an advantage to take away the throne or do something dangerous to athy
yeah basically why athy was so sheltered since she was younger is so that she wouldnt be exposed to public criticism. cause even claudes the emperor he wasnt originally the heir to the throne and is also the son of a concubine. plus his lover was a dancer from another country with no noble background (atleast none they know of). so in his own way, he "protected" athy by always keeping her with him. thats why when athy heard the nobles gossipping she was confused cause claude made sure shed never hear those gossips

can someone explain how claude was protecting athy? please?