Both the premise and the art of this manga are rather simple, and yet, It's one of the best romcoms I've seen as of late, the interactions between the two main characters are far more engaging than most of all the other romance mangas I've read, but I can't even point my finger as to why that is.
Most romance manga depends on using the same generic cliches over and over again, going through a checklist basically, so I feel the situations here are more realistic than most.
Although in my opinion what
really makes this one better than most romance is that the characters are not braindead morons or unbelievably dense, you can see the characters act like actual family, and the two protagonists are not dense, they're at best just naive and act like real children their age.
Hell, just compare to most incest manga, many of them are actual sister or even their own mother wanting to pork the male mc, this one is mostly one sided because the dude barely entered puberty, of course he'll feel sexuality confused when the cute naive dark skinned tomboy cousin is all over him, what boy his age wouldn't?
Plus although not as common as one would believe, cousins getting together isn't that weird in Japan, which probably helps too.
At best the most we have of incest besides that is the girl shipping the two, but even in-universe she's considered a weirdo.
I guess the point I'm trying to make is that the interactions feel natural and realistic, which makes it more engaging than another generic romance that goes by the numbers and lowest common denominator with forced drama.