In the distant future, mankind has advanced into an age of technological supremacy, where magic is a lost art only mentioned in fairy tales and nursery rhymes. Living in such a world is Light Inverse, a youth who dreams of sorcery…. but suddenly, his home is attacked by mazoku! With modern weaponry proven to be ineffective against the monsters, all hope seems to be lost…. Until Lina Inverse and Gourry Gabriev are suddenly transported to the future from a mysterious shrine in their time. Can Lina bring magic back to this land…!?

Futakoi Alternative tells the story of Rentarō Futaba and his detective agency. One day a set of twins, Sara and Sōju, show up at his doorstep. They move in with him and work as secretaries for his agency.
Classifying Futakoi Alternative as a specific genre is extremely difficult, although at its core, it is most similar to a romantic comedy. The first handful of episodes are lighthearted, but the series becomes more serious as it approaches its conclusion. The criticisms about the show is normally the same as its accolades: Namely, that it never settles completely into any one genre or style and switches between them from episode to episode (being almost equal parts romance, action, scifi/fantasy and comedy).
-wikipedia