Amagami SS: Sister

In this fun, light-hearted Special episode, Miya Tachibana attempts to figure out why her weird and slightly perverted older brother (Junichi) has such a friendly relationship with many of the girls in his school, yet can't manage to find himself a girlfriend. Fearing he might become a bum later in life and lose his job, she decides to stalk him to find out if there's more to him than what she sees at home.
The episode is titled "Imouto" (Sister) and is available only on Blu-Ray in Volume 13 of the Amagami SS anime series.