if i remember it correctly , Art is Brook's best friend since for ever , he is some what a player and he was courting Sara . Brook had a sister who was going to school oversea and Art live with her as a guardian ( since she is his best friend's sister , Art treat her like a sister as well) . Brook thought Sara is those mistress type of girl and try to prevent his friend from dating Sara. Art and Sara think Brook is a bad person . But really he was just looking out for his friend , Art had impregnated a girl back in his college year and Brook had been taking care of Art 's daughter and Art didn't know about this. Art was in Aemerica when he heard that Brook had marry Sara ( i think ? ) , he was anger and rape Brook's littler sister . Later on , Sara finally realize the good deed that Brook had done for her family and forgive him . Art also found out he had a daughter and became a good father and took responsible for Brook's sister.