Perhaps Nan was a character who was unjustly treated by Ro-han or he was someone that connected Ro-han to events that can never be made public, or perhaps even both.
Regardless of his identity, he didn't seem to be lying about playing a crucial role in Ro-han's life.
The record which Hans recalled was an analytical piece that attempted to trace the progress of the mythical Divine Bandit through his handwritten letters.
In more than one of those, he talked about having two brothers, one of whom had a mysterious background and remained unquestionably loyal to him throughout his journey.
Although the handwritten letters made it seem like that, when he didn't find that name being mentioned anywhere else in his biographies, travelogues, and memoirs, it slipped out of his mind.
