The Secret of the High Sales Meitantei Conan : Season 1 Episode 225

A boy named Rintaro asks the Detective Boys to investigate on a strange man named Yuuji Kamekura. Rintaro explains that Yuuji appeared one day at his family restaurant claiming he owes Rintaro's grandfather a favor and would like to work at the restaurant. Yuuji soon after begins living with the family and helps them improve the restaurant to the point the family are constantly busy with the customers.