Tenchu 2. hehe j/k
I think there's a couple of tenchu games that only came out in Japan called something like "tenchu shinobi gaisen" and "tenchu shinobi-hyakusen. I don't know how you could get a hold of these, except you can try E-bay or EBworld.
Note: I saw these games listed on a cheat code site and I saw the name Rikimaru in a cheat for Tenchu Shinobi Gaisen, but I didn't see anything on the other game that leads me to believe its part of the tenchu series. You should investigate if your interested.