Mashin Eiyuuden Wataru

魔神英雄伝ワタル

The story is about a 9-year old boy named Wataru Ikusabe that is magically transported to a magical realm of the gods called Soukaizan which he is supposed to save. In his quest to save the realm, he manages to transform a clay sculpture into a somewhat autonomous (small) Super Robot. (Source: Wikipedia)