Spring and Summer are sisters who work at a maid café alongside their younger sibling Autumn in the episode "Tanks for the Memories!" While Autumn had a thing for Brock, he was actually more interested in Spring and Summer. Spring's notable for serving milk from her Miltank to Ash's group, and she later enlisted Brock's help to introduce Autumn to her own Miltank, Ilta.
When Autumn went off with Brock, Spring and Summer roped Ash and Dawn into helping out with the café customers. The pair showed up again briefly in the ending credits of "Memories are Made of Bliss!"
Content compiled by AnimeList.moe from publicly available sources.
