Chill dude! He's not harassing the kids right? Maybe he just like kids? Lol. Maybe that's the reason why the story about Nikaido's sister was written. To hint that it's because of her, so the series won't be dragged to darkness. Cause isn't it suppose to be something funny and lighthearted?
That Nikaidou......I don´t know what to say (⊙…⊙ )