Soshite Sekai ni Heiwa ga Otozureta.

Jun Hiiro, a superhero, was facing down an alien hoping to invade Earth when the creature got a call on its cell phone, telling it to call off the invasion... and subsequently ending Jun's career. Now a nobody, Jun lives a boring daily grind of sleeping, eating, and going to work, until one day he finds a tiny alien who's unable to pay for his sister's hospitalization costs. Once a hero, always a hero? Jun sets forth to do whatever he can to help his small nemesis.