Y’all know how in writing successful stories, you have to understand your characters? Like you need a clear view of their motivations, personality, etc. And in Princess Tutu, Fakir repeatedly says he can’t seem to write a story about Mytho. For one, he’s paralyzed by the responsibility of the possible impacts writing has, especially with the chances of it becoming reality.
But also it could be considered that he doesn’t know Mytho well enough. He’s spent years at Mytho’s side, but that’s when Mytho’s an empty shell without his heart. The only thing about him is that he selflessly protects others, but that’s it. And when he started getting pieces of his heart back, he was soon corrupted.
But Fakir spends most of his time with Duck. They frequently spend time together, fight together, etc. He knows her. He’s able to connect with her thoughts and feelings. It’s him who’s able to comfort her when she sinks into the Lake of Despair because he understands her fears and doubts. And it’s Duck who he writes about. So in a way, his ability to write about her is a testament to how well he knows her.