To LOVE-Ru Darkness

As the encounters between the residents of the planet Develuke — represented primarily by the female members of the royal family — and the inhabitants of Earth — represented mainly by one exasperated Yuuki Rito — continue, Rito's hopes of a peaceful, uneventful life are set aside:

The junior princesses Nana and Momo transfer to Sainan High school on Earth to learn about Earth culture; where big sister Lala can keep an eye on them.

But when the manipulative Momo decides to pursue her crush on Rito, she proposes her harem plan, pointing out that as the future inheritor of the Deviluke's throne (once Rito marries Lala), it would be normal to have many concubines, including Momo herself (so the plan) and all the other girls Rito may fancy, including his earthen crush: Sairenji Haruna. Nothing shall stand in the way of Momo's plan, much to Rito's discomfort.

To complicate things the legendary assassin Yami, the Golden Darkness, is still (peacefully) keeping an eye on Rito, her target.

And when Rito suddenly shows up with several possessed male high school students hot on his trail, it quickly becomes clear that some unknown party is targeting both Yami and Rito!

Luckily, the trained assassin, and the powerful Momo who can communicate and control plants have no trouble protecting Rito.

But why does the mysterious assailant want Yami to return to her old ruthlessly violent self?

And will Rito be able to juggle his emotions between the alien Lala and the refreshingly normal Haruna?

And what of Momo's harem plan?

Troubled times lie ahead of Rito...