My theory is that the quintuplets never existed and there's only one girl. The five girls represent the five parts of this one girl's personality. I mean sure, some of the personalities contradict each other (i.e. Miku not knowing how to cook and Nino knowing how to cook) but we all have bad days don't we? Maybe I'm looking way too deep into the story, but whatever.
I enjoyed it, the reason why is because it was enjoyable.
