It is believed to have been affected greatly by making MINAMOTO no Tametomo considered to be a tragic hero just like MINAMOTO no Yoshi as the main character and having Ryukyu which was treated as a foreign country back then as a setting.
源義経のように悲劇の英雄と扱われていた源為朝を主人公にしたこと、当時異国の地だった琉球を舞台にしたことが大きいと思われる。