I though Ryuk wrote Tanakas name in the book because, otherwise, Tanaka wouldn't be able to do anything with the book since Ryuk wouldn't be able to possess him. Given what's happening in the usa with the Fed printing money and Americans using it to chase American stocks and in-demand real estate, I can certainly see inflation, disguised as appreciation in certain assets, as happening.
Oh, and don't get the demon king upset, evidently, or he'll do a dick move like adding rules to a Death Note. Tanaka is smart, but he didn't see that coming or the buyer's refusal to take the book, or ryuk writing in it! Thanks for the translations!!! 😈😈😈