Really interesting video, and I find /u/FeelGoodChicken’s commentary on it just as neat:
That Japanese is archaic, the scroll passed down from the mouse says シマヲアケワタセ which is a request to “Surrender the island” written in katakana. The character ヲ is not used in contemporary language and is a vestige of the kana’s roots.
Whats more, it took me a minute or two to realize that the text on the book cover should be read right to left, 日本昔噺モモタロウ, or “classic Japanese stories, momotaro” (in case anyone has not heard of momotaro). This is very fascinating as I have never personally seen a Japanese codex in which the actual text reads right to left.