Yuusha ni Narenakatta Ore wa Shibushibu Shuushoku wo Ketsui Shimashita.

Raul could not become a Hero since the demon lord was already defeated just before his Hero exams came around. His dreams dashed, he now works at the magic shop Leon in the royal capital. One day, a young job-seeker shows up, looking for work. Now only if they weren't the child of the demon lord.
(Source: Fujimi Shobo, translated)