Okay, after watching the last episode, I think it is safe to assume that this is one of the animes that are being misunderstood heavily due to their titles. As repulsive as the title sounds, and as ludicrous the "Romantic subtext" sounds, this is one the better animes I will recommend to you.
Story: (8/10)
I thought it was going to be another anime where the title says it all: in the second to last episode, they are going to break the taboo and become a couple despite being siblings. But after watching the latest episode, however, I think it's taking a different, albeit interesting direction.
The story is about two previously detached individuals suddenly becoming siblings, and through mischievous interactions as siblings, they learn to accept and embrace each other as siblings. The romantic subtext is rather misleading here because the anime didn't really establish any kind of ship between the main duo except for random perky jokes here and there - all used for comedy purposes.
Speaking of Comedy, although sometimes it appears as a bland slice of life element, the comedy aspect of this anime is decent. Now comedy is purely subjective and I think it's unnecessary to elaborate this point further.
Unless project 9 does what it did with Higehiru, I definitely think this is going to be a enjoyable ride.
Characters: (6.5/10)
There are four characters introduced in the series so far. There isn't really much characterization put behind them yet. All the characters are half bland as majority of the romcoms flesh their characters out to be, but not to say that negatively - they are likable.
Animation: (8/10)
Soundtrack: (7/10)
I think these two elements are not worth exploring in details as they are just "Decent". If something about this anime bothers you, it will definitely not going be these two. Similarly, if you find something about this anime over the top, it will definitely not going to be these two.
Overall: (7.5/10)
I believe this anime's worth a watch, at least so far. With dumbstar firses like Kanojo Okarishimaru airing, this anime is one of the better animes of the season.
