Acho que isso é Homem herói conforme minha resposta aqui:
Orphaned American boy Joey lives with his grandmother, working at a restaurant in the West Coast city of Center City (センターシティ Sentā Shiti, based on Los Angeles), while going to school. Upon hearing of a new toy robot called the Heybo, Joey believes that getting one will make his life better, turning him into a hero to protect his friends and family. However, he cannot afford to buy it on his meager salary. His luck changes when he picks up a broken down Heybo abandoned by a school bully. He tries to fix it, naming it Heroman, but does not have any luck in getting it to work. However, when it gets struck by a bolt of strange lightning, it transforms into a giant robot, just in time to save his friend Lina from impending danger. Now, Joey and Heroman are Earth's only defense against the evil insectoid Skrugg (スクラッグ Sukuraggu) aliens, unknowingly summoned to Earth by Joey's science teacher.
Capa do primeiro volume de Homem herói manga
Reboque
Originalmente encontrado pesquisando por robô de brinquedo gigante de pobre garoto de anime, e lembrado por mim como um caso envolvendo um anime com um robô de brinquedo que virou defensor.