This OVA is divided into two parts. First one is about Torii Shoutarou following his younger sister on a date. Second one is about Christmas Eve, which Mitsuki, Yuuya and their friends spend at Kanzaki's house. Bundled with the limited-edition volume 7 of the manga. (Source: AniDB)
9Anime is the best site to watch Saikin, Imouto no Yousu ga Chotto Okashiinda ga. OVA
SUB online, or you can even watch Saikin, Imouto no Yousu ga Chotto Okashiinda ga. OVA
DUB in HD quality. You can also find Project No.9
anime on 9Anime website.