[SPOILER ALERT!!!!!]

Plot: 4/10
After read this manga, almost 80% of the initial chapters of this manga had very strange conflict fluctuations. Conflicts could come on suddenly, but they could be resolved very quickly. The climax of the conflicts really developed very quickly and ended very quickly. However, 20% of this manga was truly a crisis. Suddenly, the plot fell free becomes gloomy, full of despair and confusion, out-of-society things, etc. How did they get caught by classmates, rivals, even their own parents. Each of them resolved quite "fast" like the previous chapters but in this final chapter the conflict was much heavier and it was on another level than the previous chapters. This is certainly not strange because the plot was carried out with only 48 chapters in total, and it cannot be denied that it's quite short for a story like this.
About the ending, with very great and kawaii art, but it's immoral, yet there's no plot-twist (like "that they are not blood-related siblings" and stuff), this is a pretty smooth, yet a fair ending. They know the consequences of their decision (such as not being able to have children, getting married legally, etc.) but they stay together until the end. This is a fairly a fair ending with all the circumstances they faced from start to finish without hurting many parties. But from the bottom of my heart, some part of me really support them, and I grateful for their sail. But some part of me really reject this ending (of course, because I still have common sense which leads to this being very unhealthy socially) ALTHOUGH THIS IS JUST FICTIVE, MOREOVER THIS IS 2D, but still this part of me totally reject this ending no matter what.

Art: 10/10
spoiled with the excellent artstyle from @hanoharu who is very cute, sweet, beautiful, etc. (especially as a male reader, I really love Uta), it's been a long time since I found the imouto character again with high-socks, twintails, cute voice (depends how you imagine it), kawaii face, small-to-middle breast, proportional body posture, etc. that related to "most image of imouto in this industry" or I can say Uta is "nation imouto", but it's really nostalgic (because it's been a long time since I rediscovered a character like this) and the impact is tremendous for my heart. Of course, Ami should be an honourable mention. The kind-hearted, supportives, and straightforward gyaru.
The scenes are really aesthetic, fresh, and absolutely beautiful. It really works in detail and I really enjoy the drawing.

My thoughts:
Because of this inner struggle to accept an ending like this, it looks like this manga will be the last time I read about "sister brother romcom" because the impact of this manga is enough to make my heart upset. As if there is a conflict and fight in my heart when I think of this manga.
"You don't need to take it seriously about this manga". For anyone who says that, we have different perspectives on how to respond the ending. Some end up just plain without thinking about it, some end up with depression for couple of days, some end up with thinking about it a whole night then forgot already about it, some ended up with won't read this kind of stuff again. That's the difference. This is just a pure opinion and response from myself, do not equate yourself with others. Please take note of that.

Overall, it's 6/10, fast-solved conflict, most-of cute funny romcom with great arts, high gap level on conflict in the final chapters, fair-ending which made conflicts in the heart, manga with biggest impact, to the point that I won't to read the manga about "brother sister romcom" again for temporarily, even forever. This may be the last manga that I read about "brother sister romcom".