The CO2 breathers

What happens when a mad scientist makes a potion that allows humans to breathe in carbon dioxide and out oxygen? Is this the end to global warming? Alas, the scientist's lab blew up, leaving no trace of the potion.Or was there? Droplets of it had flew across the location, entering some of the people's bodies. What will happen when changes occur and they have to flee with only one person they love?
Characters taken from UtaPri, Plastic Memories, Love Live , Owari no Seraph and Hibike! Euphonium
Yuri. Yaoi. You have been warned