The Futaba Detective Agency, being run by Rentarou, who has taken over the family business, after his father's death 3 weeks ago. Along w/ Sara & Souju, his live-in identical twin assistants. He ends up running afoul of the local Yakuza. (Source: ANN)

Struggling yet brilliant teenager Minato Sahashi has failed his college entrance exams for the second time, resulting in him being regarded as worthless by those around him. However, the course of his seemingly bleak future is altered dramatically when a beautiful, supernatural woman falls from the sky and into his life. That woman, Musubi, is a unique being known as a "Sekirei," a humanoid extraterrestrial with extraordinary abilities. These aliens are known for kissing humans carrying the Ashikabi gene in order to awaken additional latent powers deep within. Recognizing the potential within the seemingly insignificant youth, Musubi kisses the bewildered Minato, initiating a bond between the two of them. This drags him into the high-stakes world of the Sekirei, where he and his new partner must compete against others in a battle for survival called the "Sekirei Plan." However, unbeknownst to the contestants, there is far more at risk that what the competition initially entailed. [Written by MAL Rewrite]

The second stage of the battle royale known as the Sekirei Plan is underway. Shintou Teito has been closed off; no Sekirei or Ashikabi may leave. Minato Sahashi and his harem of Sekirei must now prepare to fight new battles as changes to the rules are put into place. However, not all groups will return to the battle: some Sekirei are loved very much by their Ashikabi partners, who would rather forfeit the prize than see them perish. In the midst of the action, someone close to Minato may be more involved than he had ever imagined, and threats lurk around every corner. There are even rumors that the "Single Numbers," the most powerful type of Sekirei, have entered the fray. In the eyes of the "Game Master" Minaka Hiroto, everything is proceeding according to plan. [Written by MAL Rewrite]

"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.