5/10- Pretty mediocre.
This show is the definition of "meh". I haven't something this boring in a while. I really should have dropped it around Episodes 4 or 5.
The characters are very poorly written. They all have barely any personality. Characters do stuff that would get you in jail. The worst part is that it's not even slightly funny to be considered a joke. The little sister character undergoes assault but it's played for cheap comedy.
There is some potential here in regards to our main character- Itsuki's relationship with his father. His father remarried rather quickly after his mother's death, which has been a point of contention between them. He stops talking to his dad after that and moves out. They have a pretty broken relationship but we don't really see any progress on it. It's barely even mentioned. This could be an interesting venue to explore Itsuki's character but we spend most of the time seeing our characters either play board games or harass each other or make unfunny jokes.
The backdrop of the story is the manga industry and what it would take each our characters to become successful manga authors but its not the focus. It's part of the background, but the story spends very little time on it.
I almost forgot to mention the title is kinda misleading. There really isn't enough little sister in this show, so consider yourself warned.
Unfunny, mediocre and mediocre at times. All in all, this is very skippable.
TLDR- 5/10. Mid, skip it.