Arisa and Mika, they are the Nanase sisters and the school super-idols, they are the hottest and cutest girls in the school. Sousuke is a normal student that as all other boys can only look at the super-idol sisters from afar. Sousuke likes Arisa but can never hope to even speak with her. One day Mika tells him she want to speak with him after school. After school he meets with Mika and Arisa and they tell him they have become siblings!! The truth is Sousuke's father who is an adventurer and the Nanase sisters Mother who is an archeologist met at an excavating ruins in South America, fallen in love and married.
Mika, Arisa and Sousuke are now siblings and will live under the same roof from now on...Sousuke got to be careful not to be caught masturbating by Mika or Arisa....or who knows maybe they will give him a helping hand?...how about taking a bath with Mika?...siblings do bath together after all...