These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Kono Naka ni Hitori, Imouto ga Iru!
Big Lipped Alligator Moment: Pretty much every time the School Newspaper Head makes an appears. It is pretty much nothing more than watching her insane antics of over enthusiasm for a minute or so before the plot goes on.
Idiot Plot: The whole Yuzurina not being his real sister could have ended right there in the pool when he announced her to the group. This is because Mei, who is fully aware of who his real little sister is could have just spoken up and stated it wasn't her. But she remains quiet the entire time on the subject.
Actually, revealing that Yuzurina wasn't his sister would have been counterproductive. At that moment, Yuzurina had a DNA test backing her up and Shougo still trusted Seri, so saying anything would have put Mei in a very unfavorable position: losing Shougo's trust and alerting Yuzurina of the threat Mei presented.
Stop Helping Me!: Shougo runs away from Miyabi and Konoe in episode 3 due to their insistence on "training him to like girls".