@cleitonevil You could have just said "that doesn't have a sibling," because by your definition the Ninomiyas don't exist in this manga. It's a younger sister/older brother pair.
Also, is everyone so desensitized to ridiculousness that no-one is mentioning the magic ice cream that somehow unbuttoned and opened her shirt before landing between her breasts?
Yet, huh? So, you're going to think about it at some point? Oh, lemme guess, you're going to decide on twins. Just keep the twincest chain going. I approve of that desire.