lol, why do you think torrents are illegal in Japan?
Anyway, you're probably not going to find what you're looking for. The Japanese don't use torrent trackers like we do. They use the
darknet. A real popular file sharing program they use is called
シャレ(洒落) or Share, pronounced Sha-re. It's based on using the
Freenet, well, just read the links, it's hard to explain. There's nodes and keys, but to even access these networks you have to communicate (in Japanese) on Japanese message boards and earn trust.