Complex sentence: Nagako attended the Girls'Department of Peers' School in Tokyo (now Gakushuin) with Crown Princess Bangja of Korea (then known as Princess Masako Nashimoto).
Split into simpler sentences: Nagako attended the Girls'Department of Peers' School in Tokyo (now Gakushuin). Among her classmates was Crown Princess Bangja of Korea (then known as Princess Masako Nashimoto).