Keita has two older step-sisters, Ako and Riko, but since they aren't related by blood, they love him in a lustful way. After a mishap at school, Ako and Riko finally confess their love to him. Keita dislikes the thought of seeing them other then brother and sister, but as he tries to enter the same school as his sisters, he slowly becomes attracted to them.
Well, this is an anime with a plot which some people, by watching the anime would have many opinion and thigs to criticise, but leaving that apart, it´s a very good anime, with a good fan-service ^^ and tough the story it´s totally simple, it´s entertaining...
I can´t say that "I recommend it", just watch it if you want and then you decide if you like it or not...
PS: If you like the first episode, in that case I can reccomend you to see the others.. ^^