The movie starts with the Sazer-X playing basketball. All of a sudden a flash of lightning strikes the earth. They headed for it, and discovered a boy. The boy was Riki, who assumed to forget everything. On the other hand, Remy informs the Sazer-X that a giant monster, 'Mecha Giant Beast Bulgario', had approached the Earth and were destroying buildings. The Sazer-X defeated the monster anyway. But then something flashed into their eyes, Takuto had mistaken it as a Cosmo Capsule. It was, in fact, a Bosquito existed inside Bulgario, which was later explained by Professor Horiguchi.—wikipedia