OK, this is my first movie to search :
I saw this anime around 1981, maybe (spanish TV, sorry), so is earlier, the movie seems to be very old. The boy have tipical “ninja powers”, a (magic?) sword and must to kill a big dragon or this dragon go to destroy the entire village, but I don’t sure about this. I don’t remember much from the movie, except the end : The young boy understands that the dragon and he have a connection, so the boy cut their own throad to kill the dragon… Or something like that. I remember the scene when the body of the boy fall into a… Waterfalls ? I think this is correct, but I was 9 years old !!
Is not “Tatsu no ko Taro” (“Taro, the Dragon Boy“) nor “Shônen Sarutobi Sasuke” (“Magic Boy“)
Thanks a lot