Kabamaru the Ninja (1983)

Kabamaru is a young boy raised and trained by his grandfather as a ninja. After the sudden death of his grandfather, he starts living with Mai, his grandfather's mistress, who is a school director. He is asked to help out on struggles against other schools, as he is master of the ninja mystical arts. As time passes he will make lots of friends as well as enemies, and fall in love with Mai.