I have seen this anime on TV as a child, dubbed in Arabic (so I couldn't tell you what the character names are). This was during the early 80s and I don't recall much of the detail.
The protagonist is a boy, always dressed in a red kimono and long black hair tied up and armed with a katana.
As a ninja he was able to transform to different animals (I recall a very large fish).
Wish I had more details, but it was long ago and in a language I did not understand.