The Devil Is a Part-Timer! by Satoshi Wagahara. A Comedy manga rated Teen, published in English by Yen Press.

Defeated by the forces of good, the Demon King Satan escapes through a portal and lands in modern-day Tokyo, powerless and broke. Now going by Sadao Maou, he takes a job at a fast-food restaurant and works his way up the corporate ladder, while the hero who defeated him follows him to Japan.