What was the Japanese exclusive content in Cave Story 3D?

According to this Siliconera article, this bonus content comes in the form of alternative playable characters from the three games mentioned in the articles above:

Cave Story 3D is set for release in Japan on July 25 and this version has a few guests not in the North American release.

You can play Cave Story 3D as a handful of retro heroes like the protagonist from Falcom’s Dragon Slayer.

dragon slayer cameo

The lead character from Hamster’s arcade game Crazy Climber is in Cave Story 3D too.

crazy climber cameo

You can also play as one of the rebelling famers from Sunsoft’s Famicom game Ikki.

ikki cameo