The main target for this act is to stop a file sharing program / network called Winny. Winny is one of the top File sharing program / network in Japan.
The trick is that many (but not all) Japanese users have moved onto a replacement program called Share and other software, after vulnerabilities in Winny's anonymity features were discovered. Then vulnerabilities were discovered in Share, too, so some users have moved onto yet another replacement.
The creator is facing similar claims to that of the Bittorrent creator, where he has created a tool that can be used to share files with the advantage of being anonymous.
The creator actually already faced those claims and was given a 1.5-million-yen (about US$12,000) fine. He has since starting working a SkeedCast, a file-sharing program that is used by Gonzo and other companies for authorized file-sharing. You can find more information about all this
here.