Nathan Mahler appears to be one of the oldest of Diva's chevaliers, though when and how he became one is unexplained. Towards the end of the series, while talking with Amshel, Nathan states that the world exists to showcase Diva's beauty, as was predestined before she was born. When Amshel says Nathan talks like he was there, Nathan says he was and that before Diva and Saya were born, there was their "mommy" and her faithful chevalier. Nathan later tells Saya that the only thing Diva actually wanted was to have a family.

In the original Japanese series, Nathan often speaks in a manner usually employed by the feminine gender, such as using kashira and wa. In the Sony English dub, this is represented by Nathan speaking in the manner of a stereotypical homosexual character. Unlike the other chevaliers, Nathan rarely participates in battle. Behind his seemingly effeminate and lackadaisical manners, Nathan may be the most powerful of the chevaliers and will assert his dominance over his younger "brothers" if he feels he needs to. He is the only one of Diva's chevaliers who can make Amshel back down if he chooses to, and the only one Amshel rarely attempts to manipulate. He plans not only to destroy Saya, but to do it in a "stage" prepared only for the occasion. This desire results in his stopping some battles between Saya and his brothers, much to their annoyance.

After Diva's death, Nathan asked that Saya kill him, changing into his chiropteran form and allowing Saya to slice through him with her sword, although he is not seen crystallizing. At the end of the series, he is seen in his human form amongst some reporters outside of Van's trial.