Metal Max 4: Gekkō no Diva

The story took place 50 years after the destruction of human civilizations by mad supercomputer Noah. The protagonist (default name "Hinata") is a young boy who is living peacefully with his foster sister Sasha and foster father Gib in desert islands. One day, a group of mysterious army attacked their island. The protagonist and Sasha escaped but Gib get abducted. The protagonist now must save Gib before the villains use him to obtain the indestructible mobile fortress. (Wiki)