(This is a review to the manga.)

Similar to "Yuri is my job", the concept is a catholic/christian setting with only girls, who are calling each other "sisters" and that's somehow an intimate way of saying you're together, basically. 
I don't really know what's up with that combination for yuri stories... I don't mind the religious part, but the incest-kinda-stuff is a bit concerning?

I'm just confused on the world setting, though. It seemed at first that they're normal teenagers, who like to experiment out together. However, there's a competition in July, which is really important and everyone takes it serious and it's all about giving the school a good reputation... but it's so gay. Is it in a world where everyone is gay and it's normal too for christians? Like an AU? Or are the teachers simply completely oblivious to the fact, how gay this competition is? Because they literally are called couple, have to win together, there are no boys, they will get the status of a Prince & Princess afterwards and serve as idols for everyone else. 
I need a bit of more world-building. 

Also, there's a lot of sexual assault going on...

It ended on a cliffhanger though, and only has 2 volumes anyway, so I might as well finish it.