Maybe this is just like a flashback and the reason why Mutsuki always lowering her guard around Haruki. You know, Mutsuki always show her "perfect side" to her sisters and at school. I think it's still reasonable this ch is bonus short story collection.Great chapter, but it's strange that this is a .5 chapter, you'd think this would been in the main story instead of tucked into a short story collection. But I guess each .5 chapter will focus on each character?