Sahashi Minato is very intelligent, yet due to his inability to cope with pressure has failed the college entrance exam twice. As a result he has been branded an idiot and loser by many. One day after talking to his yet again disappointed mother he comes into contact with a girl named Musubi, who was under attack. The girl runs but takes him with her and soon finds that Minato, while unknown to him, is an Ashikabi, one of the mysterious set of masters that have the genetic trait that can become partners with some of the 108 cute girls, buxom women, and bishoujo called Sekirei. Only by means of such a partnership can the Sekirei use the full potential of their powers to win in the competition held by the ominous MBI corporation.

[Source: Anime News Network]

"Kusano's first errand" - A ten minute OVA that came along with the 6th vol. limited edition of Sekirei. Kusano finally tires of nobody admitting her as Sahashi's potential wife, so she insists on joining Musubi and Tsukiumi on their shopping race to show her abilities. An iffy day ensues.

In Tokyo in the year 2020, Sahashi Minato has failed the college entrance exam twice, is awkward around women, and unemployed. One day, Minato meets a girl named Musubi, who literally falls from the sky.

Minato soon learns that she is one of the Sekirei and he is her Ashikabi, a human with special genes make it possible to form a contract with Sekirei. This binds the Sekirei to him and allows them to use their full power in the Sekirei Plan, a dangerous and deadly competition organised by Minaka Hiroto, chairman and founder of the mysterious and powerful MBI Corporation. Minato finds out that being the partner of a beautiful girl is not all fun and games, especially when it turns out that an Ashikabi can have more than one Sekirei partner — and that is where the real trouble starts.

[Source: AniDB]

Episode 0, consisting of two segments: "Sekirei Shindan" (鶺鴒診断) and "Sekirei Yoka" (鶺鴒余暇), of Sekirei: Pure Engagement included on the first DVD/BD volume.