Quiet and withdrawn, Nagisa is the Child of Water, the guardian of the Cup of Life, and the Keeper of the Lighthouse of Cabra. For forty years, he has devoted himself to the study of water magics, the maintenance of the Lighthouse, which provided the only safe route past the Rebman Maelstrom, and to the search for the Demi-Jewel of Water.
During this time, he also secretly married Princess Gabrielle of Ember and they had a child together, Princess Shinobu Minor.
Fate saw fit to deprive him of a role in solving either the problem of the Maelstrom or the problem of the missing Demi-Jewel. While it remains unclear as to why the Rebman Maelstrom came to an end, Prince Lucien has found and claimed the Demi-Jewel of Water for himself.
Their meeting at the Marching Ball led to an argument between the two, one of the few known examples of Nagisa actually becoming angry. It also provided a rare reminder of the fact that Prince Nagisa is a lot more nimble than he looks, as Prince Lucien proved unable to successfully slap him in the face to provide a challenge.
Despite this, Nagisa and his wife, Gabrielle, upon learning from King Tylor that Prince Lucien had fallen under the control of Bloc Rebmaquois, set out to confront Lucien, and successfully broke the Bloc's hold on him and his female assistants.
Nagisa was nearly slain by the Abyss-controlled Prince Saionji recently, but has since recovered.