Shoujo no Kami no Ryuushi

Those of the Dark Matter lived by swallowing others who did not accept them.

In the midst of all this, Nemophila---the princess of the Dark Matter---fell in love with Sho, the sole survivor of a planet that she had destroyed for fun, and whom she'd spared as a joke.

This is the story of how dark matter, which is "invisible" to everyone, came to acquire "mass".

[Translated from official website]