Anime Crossover: A False Life

Everyone has an alter ego inside them. They may all be different, but they are all dark, because only an unsatisfactory life can create the soil in which they find rest... The darkest of all are those who pretend to be cheerful. They seem happy, and even when they feel down, people just assume it's a passing low. Their alter egos rage inside them. They aren't afraid of bloodshed; quite the opposite, they love the taste of blood. When they burst free, the world is turned upside down... But that's only one kind of alter ego. There are also those, like our protagonists, whose souls become attached to them and turn them into alter egos. Similar examples: Soul Reapers and Hollows Jinchuriki and tailed beasts And Kyoko Mogami and her Pandora grudge spirit~ …A saintly big sister and a violent, awkward little sister who never says what she means. Interested? This isn't yuri... ah, never mind.