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.
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.
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.