Natsu

and Summer are two characters of the day who appeared in Tanks for the Memories! (DP062).

Spring and Summer are two sisters who work at the Maid Café along with their younger sister, . While their younger sister had developed a crush on , Brock was more romantically interested in them. Later, Spring served milk from her Miltank to Ash and his friends. Spring later asked Brock to help Autumn to get to know her Miltank named Ilta.

While Autumn was out with Brock, Spring and Summer asked Ash and Dawn to help serve the customers.

They reappeared in the ending credits montage of Memories are Made of Bliss! (DP191).

(Source: Bulbapedia)