The The Devil Is a Part-Timer!, Vol. 16 (light novel) — Satoshi Wagahara

Do you want fries with your hellfire?To fight Ignora, Maou's group must restore Devil's Castle to its former glory. However, because of his schedule at MgRonald, Maou needs to save time on his commute by staying in Japan. While he's stuck there, Suzuno, Laila, Albert, and Rumack travel to the Northern Continent to retrieve the Spear of Adramelechinus. Maou, unable to help them -- and living the bachelor life, alone in his apartment for the first time -- receives chocolate from a work trainee, but how will the other women in Maou's life react to that news?! The Devil King faces off against his next enemy: Valentine's Day!