After an encounter with a hated rival during a festival she'd been looking forwards to all year, Rarity learns that sometimes her anger blinds her to what - or rather, who - is most important.
When Rarity discovers Sweetie Belle has a serious health problem, she does everything she can to help Sweetie work through it and become healthy again.
During one particularly stressful day, Sweetie Belle gets into Rarity's makeup. Rarity demands an explanation. The answer isn't quite as simple as one sister trying to emulate another.