Drugstore in Another World: The Slow Life of a Cheat Pharmacist (Manga) Vol. 10

Demon King Ejil acts tough, but he wants to be first in lake spirit Vivi's heart. So when Vivi starts her new job at Kirio Drugs, Demon King Ejil gets jealous of how close Vivi is becoming with her new coworkers. Lucky for him, Reji has just the right potion! To reward all of Ejil's hard work, Reiji makes him a medicine that will grant his deepest wishes. Ejil tries to use it to get closer to Vivi, but the obstacle to her heart isn't her new friends--she's got one huge worry. So huge, in fact, that the only way to solve it is to become gigantic!