No Ace Attorney game has even come
close to M-rated. Even if this game is the darkest in the series, I highly doubt that rating is warranted. This has to be an exaggeration.
"Violence, Blood, Suggestive Themes, and Language" - which are actually the very same content descriptors assigned to the first game in the series back in 2001.
Which is odd, considering there has been no language in the Ace Attorney games. The worst they've gone was the use of the word "damn"; which isn't even a curse.
As for suggestive themes (in the first game), it's more like mild suggestive themes. The worst was some very minor boob jiggling.
I bet this game won't come close to actual M-rated content at all, as that would be a HUGE leap for the franchise. From what I've seen in the demo footage, the playful humor is still there at the very least. That would not mix well with extreme gore and excessive cursing.