The story follows , an average student whose life changes when his father reveals he has arranged a marriage for him. Shinichi discovers he is actually engaged to four non-human "princesses" simultaneously:

An airheaded Arachne (spider girl) aristocrat.

A Lamia princess from a military empire. Proxima: A noble and serious Centaur knight. R-Komadori: A mechanical/android princess.

The narrative stakes are high: if Shinichi fails to choose one of these girls as his bride, it is claimed the rejected ones will destroy the world.