Jaco the Galactic Patrolman, by Akira Toriyama, Translated by Tetsuichiro Miyaki.
Viz Media, Manga.

A gruff scientist named Omori lives alone on an island, attempting to succeed in his bid to travel in time. His tranquil life is interrupted when a spacecraft crash-lands off the coast, stranding an alien named Jaco, who has a penchant for grandiose displays of exhibitionism. As he constantly reminds Omori, he's no ordinary alien: He's an elite galactic patrolman who has been sent to Earth to update his species on humanity's progress. He can even fly ("but only in emergencies"). The Earth then faces a dangerous threat, and only Jaco can help. But at what cost? Produced by the creator of "Dragon Ball Z," Akira Toriyama, "Jaco the Galactic Patrolman" makes saving the planet look like a walk in the park.