Sekirei

(Note: All Sekirei are 18 and up, regardless of appearance.)

This is a world where alien girls called Sekirei find their lover called Ashikabi, one of the mysterious set of humans that have the genetic trait and can make a contract by kissing the Sekirei; this binds the Sekirei to the Ashikabi and allows them to use their full power in elimination battles with other Sekirei. Made up of 108 cute girls, attractive buxom women and bishōnen, the Sekirei fight in a competition known as the "Sekirei Plan" organized by Hiroto Minaka, the chairman and founder of the mysterious and powerful MBI Corporation in Shinto Teito.

The Sex Note found itself falling through the air, cascading down and falling in Shinto Teito.

The question is, who ends up stumbling upon this magical book?