The Devil Is a Part-Timer!, Vol. 9 (light novel) - Satoshi Wagahara

When Emilia the Hero is in danger, she finds an unlikely ally in the Devil King! Unfortunately, with Ashiya kidnapped by Gabriel, the team is seriously lacking in manpower. Maou and Suzuno partner up on a rescue mission, traveling undercover through Ente Isla, while a mysterious girl claiming to be Alas Ramus''s younger sister tags along. Meanwhile, Emi and Alas Ramus get caught up in the middle of Olba''s schemes. The barriers between angels, demons, and humans-and ideas about who''s good and who''s evil-come crashing down!