The story is about Yuuki Rito, a high-school boy who cannot confess to the girl of his dreams, Sairenji Haruna. One day when coming home and sulking in the bath-tub a mysterious, nude girl, appears out of nowhere. Her name is Lala and she comes from the planet Deviluke, where she is the heir to the throne. Her father wants her to return to her home planet so she can marry one of the husband candidates, but she decides that she wants to marry Rito in order to stay on Earth.
A casual day for Rito and the girls becomes something more as a Devilukean drink has a peculiar effect on Sairenji.
Rito picks up a strange device that Lala dropped at school. The alien technology has an interesting effect that will leave Rito exhausted and a little mousy.
Nana retreats to her own private Safari to contemplate Mea’s true form and the words she said that may forever change their friendship.
Rito and the girls are ready to have a blast at the Summer Festival. But as Momo is enjoying rare time alone with Rito, a dangerous introduction is made.
The day after an awkward mishap, Rito bumps into Yui while boarding a train and another sticky situation occurs. Later on, Mea is invited to dinner at the Yuuki house.
Momo fantasizes about alone time with Rito, only to be interrupted by Nemesis. Later on, the bath becomes a hot spot as Momo finds Rito with someone unexpected.
Momo is concerned about the distance between Tearju and Yami, and she tells Rito as much. He decides to speak with Yami, but Mea’s contribution may be the tipping point.
Rito and the girls are enlisted to help out at the Tenjouin mansion. The girls dress up as maids for the task, but a mysterious sword turns the mansion into a battleground.
Lala wants to help Rito and Haruna get closer, but Momo’s plan needs Lala to be the first wife. Utilizing a dating sim, Momo educates her sister about expressions of love.
A vacuum Lala invented goes crazy due to Oshizu’s powers; it’s sucking up the girl’s clothes! Mea is forced to make a decision as the invention’s core threatens the school.
With everyone's acceptance of Mea, Yami is coming to a realization that will change everything; Nemesis capitalizes on this and pushes the situation to a breaking point.
Yami’s transformation takes everyone off guard; her goal stays the same, but nobody expected her methods. Mea resists against Nemesis’ hold on her body in an effort to help.