written more than 2 letters of his name, but there was a warning in the book someone had written saying not to trust Ryuk.
I had assumed that they were trying to imply his name wasn't actually spelled "Ryuk" but phonetically that was close enough.
So 'Ryuk' would give you an idea of how to pronounce his name but wouldn't kill him if you wrote it in the notebook. Honestly, I don't know why they didn't just have him say you can't kill Shinigami with a Death Note, like in the source material, but whatever. ---