The Underground Tennis Tolurnament: The Campbelldon (S01E22)

The secret files called the Zacharis Dossier may cause a war between the East and the West. In order to obtain a painting that is supposed to be the hiding spot for these files, Loid and Fiona enter an underground tennis tournament run by the owner of the painting, Campbell. If they win, the art piece they're after will be presented. Loid and Fiona enter as a married couple and play various skilled players including pro players! (Crunchyroll)