Yuusha no Party ni Eiyoushi ga Kuwawatta!

The hero Kavin is on a quest to save the princess from an incurable illness, but his stomach problems are dragging his party down. After a particularly bad case of the runs, he meets a woman named Hanae at a restaurant, who is very knowledgeable about nutrition, and helps him have a light meal that won't upset his stomach. Moved by this, Kavin immediately decides to add Harue to their party to make sure they're all eating properly.

(Source: Kadokawa, translated)