Ninja Boy 1983

After the death of Saizou, Kabamaru's horribly strict grandfather and iga ninja-sensei (teacher), an old lady Ran Akoko claims that she received a letter from him asking her to take care of his grandson. So Kabamaru runs off with Lady Akoko to the big city Tokyo to gorge himself on yakisoba, Ramen, chow-mein and attend a regular school which turns out to have weird quirks of its own.