I thought it was better to warn but it does have some great moments and music^^
Actually have no idea, series are still ongoing. The girl from normal world was accidently tranformed back in time and for some reason everyone are females, she herself was damn confused. There seems to be some experiment happening or something, at least going by some flashbacks.
Well if believe series explanation... kids are found in cabages, banbooks and in all other ways that parents tend to tell kids when they ask "Where do the children come from?"
So if you happen to be bored someday, you can try to check first 3 episodes and see how it will suit your taste
Especially if you want to watch some comedy. Also despite the looks, they are not very fanservice full either despite having such huge female cast.