Are you pertaining to "silence"? I think it's Iheon who introduced it to huimin in the drawings, remember he's the first one to discover that they're both just characters in a book?
Yes, but Iheon finds it in the imaginary world built by Huimin's drawings, unknowing of where it came from. The origin of the book is never discussed. It just appears before Iheon in the library. Him and Huimin weren't born from the book -- the BOOK was born from their lives in the real world.
That's why I'm wondering how it even conjured itself in the first place -- it was a fake world where the only people that were real within it were the two of them, and neither of them wrote it.
So the only explanation I could think of is that Huimin locked his memories away in book form and subconsciously wanted them to be unlocked, which is why it showed itself to Iheon.
i still wonder who the f wrote the novel in huimin's imaginary world. like was it a manifestation of the memories huimin locked away??