The siblings' romance (not their personalities) is a lot like Ore no Imouto ga Konna ni Kawaii Wake ga Nai (Novel) with the roles reversed. Essentially, the premise is that were closer when they were younger, but the little brother started to act cold (and also, sleep around with random women... but in a self-abandoning sort of way, not feeling anything for them) toward his sister, the protagonist. She formed a bad opinion of him in return, and stopped trying to interact with him. But then one day by chance, she discovered an unusual side to him, which triggered them reconnecting. Just like in Oreimo, there's a lot of subtle characterization (like the protagonist's obsession with cleanliness) which makes you realize there's a hidden aspect to the siblings' history.
It's gold up through volume 3. The pacing is especially impressive in volumes 1 and 2. The romantic interactions are so cute and endearing, defying cliches and continually surprising you. It's impressive how the romance can be serious and engaging without ever feeling melodramatic. I mean, there's incest (not the kind that's played for laughs), secret identities, love triangles, but no melodrama...? I compared it to Oreimo, but it has none of the relationship angst that Oreimo exhibited at times. All I can say is that I'm so glad I read this manga.
The pacing has slowed down in recent chapters, though. Side characters have been more prominent, and the author is arranging for various characters to clash. I have faith that the author will let it take the story somewhere positive, but I have to say I prefer the earlier rapid and refreshing developments to these typical "build up to forceful resolution" style developments. Because the protagonist ends up being more indecisive and making more stupid decisions to facilitate that. She's usually smart and proactive (and cute!). Anyway, I expect the series to wrap up in a few more volumes, unless the story expands in scope (I hope it does! I'd like to see more happy flirting, but I fear the rest of the manga will just consist of resolving the main relationship...). To be clear, the manga remains very enjoyable.
