Now the chatter is around its age rating in Japan, which rather passed us by when we reported on the game's file size from the official Japanese website. It's a CERO B game, which is bucking the trend of mainline Mario platformers being CERO A.
While CERO A is 'content suitable for all ages', the B equivalent is recommended for ages 12 and up, though younger ages are at a parent's discretion.
Contains some content parents may not like for children under the age of 12. May contain mild sexual content, some violence, mild horror content or infrequent use of profanity.
Joking aside, it may not be the shirtless Mario that has caused this; interpreted violence or 'mild horror' could be a factor in the game. In Europe this has a PEGI 7 rating ("contains some possibly frightening scenes or sounds") and in North America it seems to have been given ESRB 10+ ("may contain more cartoon, fantasy or mild violence, mild language and/or minimal suggestive themes").
Super Mario Odyssey may have a little more edge than previous entries, or perhaps ratings agencies are a little unsure of the Cappy possession ability. Either way, Nintendo will hope it doesn't affect sales; based on how many parents we've seen buying Call of Duty for their little 'uns over the years, we're thinking any impact will be minimal.
With thanks to Spoony_Tech for the heads up.