This "Borderless" is a joint production (in the American comics I'd sometimes read when I was a kid - thus wasting time and money on horribly poorly written cr@p, but that's another story - it'd be called a "Team Up") between the three Sakamichi idol groups: Nogizaka46, Hinatazaka46 (formerly known as "Hiragana Keyakizaka46") and Sakurazaka46 (ex- Kanji Keyakizaka46).
The main cast is composed of seven members of the different groups, namely two each from Nogizaka and Hinatazaka, and three from Sakurazaka. Fans of any of those groups will surely find some added value in seeing how some of their favorite idols performed as actresses. For example, being a fan of Hinatazaka and Sakurazaka, I knew I was gonna get some good acting by Saito Kyoko and Kobayashi Yui, but I wasn't honestly expecting much from the other girls, and was therefore positively surprised by their performances - particularly by Hamagishi's - whom I hadn't pegged for one capable of acting as she did here. Kudos, Hiyotan! ^__-
Now, not being a Nogizaka fan I had no idea what to expect from Hayakawa Seira and Endo Sakura, but they did quite well too, especially the latter. All in all, the idol main cast was more than okay; alas, the same can't be said of all the supporting actors and actresses, from whom we got mixed performances instead.
The production value of this dorama is pretty high, even more so for Japanese standards.
The real problem - and the reason behind the low rating I'm giving it - lies in the script.
Although it has some (rare!) good moments, those are literally drowned in an abundance of mediocrity; the dialogues are often unnaturally verbose and the scenes frequently boring (weren't it for the musical score keeping up the tension, I would've fallen asleep more than once!) or even nonsensical - as is, for example, the way the different storylines are brought together: a moment I was looking forward to, but that instead let me down completely. Just as the "mystery" solution, which was plainly terrible imho. But the worst thing was, for me, the ending: when you write your villain as such a despicable person, the viewers deserve to see him/her *punished* at the end, NOT *rewarded* with a happy ending!!! >______<
5/10 because I don't want to be too hard, given how the girls performed.
But I'm personally blacklisting the writer as we speak.
p.s.
The best part (BY FAR) are imho the 10' or so of "Making Of" scenes, shown at the end of each episode! (LOL at least the writer couldn't ruin those! ^__-)