Rook Castle made his first and only appearance in Battle Arena Toshinden 4, as an initially playable character.
As a child, Rook had always been a fan of the Toshinden tournaments and their champion, Eiji Shinjo and after watching many martial arts movies, he was inspired to join a school of kung fu. Training hard with his weapon of choice, the nunchaku, he gradually became stronger over the years. He started going downtown and challenging other strong fighters, defeating them all. However, he met his match one day, in the form of a young ninja girl who seemed to be fighting against her own will. Although he lost, he developed an instant attraction to her.
However, the girl disappeared immediately after defeating him, leaving him disappointed. He later ran into Subaru Shinjo, the travelling student and adopted nephew of his idol, Eiji Shinjo. The two quickly became friends, journeying and training together for a while.
The pair then encountered Kayin Amoh's adopted daughter, Naru Amoh, who told them of the fourth Toshindaibukai that was soon to begin. She then showed them two invitations she had received, which were mysteriously marked with the initial "E". Deciding to enter the tournament with Subaru and Naru, Rook was determined to prove himself as the strongest fighter in the world, and to find the mysterious ninja girl again.