Minato Sahashi was living a normal life; he had just failed his college entrance exam for a second year in a row, and lived a quiet life in a single's apartment. That is, until the busty Musubi fell from the sky on top of him! She is a Sekirei, one of 108 that are destined to fight each other until only one remains; and he or she will ascend to heaven with his or her chosen one known as an Ashikabi. Minato soon finds himself in the embrace of Musubi, becoming her Ashibaki - but his life will only become more complicated. Musubi isn't the last to claim Minato as her Ashibaki, and what's worse, plenty of other Sekirei and opponents stand in his way!
Both are harems with multiple love interests. The previous seasons of Zero no Tsukaima had some fighting like Sekirei but this season particularly reminded me of this Sekirei. Both anime are about men who are caught up into a new (figuratively or real) world that they never knew existed and make a contract with a girl. SPOILER: Both men end up contracting with multiple women and have to deal with the jealousy that ensues.