Rainbow Dash woke up early one Sunday morning and found herself unable to get back to sleep, so she figures she'd hop out of bed and make an omelet for breakfast, typical Equestrian morning in the Canterlot City country side.
After a huge stint with their role models, the CMC decide that to learn their special talents, they have to take their search out into Equestria. They meet new friends, save many lives, and become an inspiration. This is the last crusade.
Scootaloo really wants to talk with Rainbow Dash, but Rainbow, caught up in her own happenings, doesn't make time for Scootaloo. This leads to Rainbow and Applejack talking about the meaning of sisterhood.
A big sister is what Scootaloo really needs right now, seeing as she decided to stay behind in Ponyville when her friends needed her most. Luckily Rainbow Dash comes to comfort her and offer support, finally assuming her role as her big sister.
Nopony said it was easy. After a terrible fire nearly claims the lives of the Cutie Mark Crusaders, Rainbow Dash has to seriously consider what it takes to be a sister when she has to face the prospect of disciplining the newly-adopted Scootaloo.
Rainbow Dash and Scootaloo weren't born sisters, they became sisters by choice. In an attempt to help Apple Bloom, Scootaloo accidentally puts the bond of that sisterhood to the test.