The World or Her

The World or Her (かかべない, Sekai ka kanojo ka Erabenai!) is a romace series written by Atsushi Uchiyama (Attsun)

Plot
Nakagawa Kouki has a crush on his childhood friend Fujisaki Ayumi. Another girl, Jindou Hikari, warns Kouki of the mysterious power of calamity Ayumi possess, and gives him a choice: To choose the world or her.