A Light Novel written by Kōshi Tachibana and illustrated by Tsunako.
In the future, spherical so-called "space quakes" have destroyed great deals of Earth's landmass. In response militaries and scientific communities all over the world have worked together to find out the origin of the occurances, to little effect.
Enter Itsuka Shidou, a young man of above average skill in school but no experience with girls. By accident he stays near the area that was just ravaged by a space quake, only to find a girl in a warrior dress who treatens to kill him. Before he can say much, she disappears. Afterward he learns that she, among others, is called a spirit. Spirits come from another world and cause destruction whenever they enter ours. Shidou is now given a choice to see how the military kills spirits, or take another option: date the spirits, make them fall in love with and surrender their powers to him so they can live among humans without fear of being hunted.
A very Datim Sim-like adventure begins for Shidou.