A pretty non-standard anime that asks tough questions
I'm writing this review as a young father with one son. I was a huge fan of anime growing up and still am to this day. I chose to speak up here because the official, staff-written review, is way off base in a couple areas.
The first being: positive messages. Throughout the first few episodes, the main conflict for our young, and might I add, female lead, is having to face a horrendous and ultimately life-changing reality. Thus, she starts off as aweak character, unsure of herslf and what she wants. But as she progresses towards the end of the season, she gets stronger and stronger, not physically, mind you, but mentally. She becomes willing to make the tough calls, strengthens her resolve and keeps good on her promises to both her family and her team. The positive message throughout the series is: the right thing isn't always the easy thing, but you'll be all the better fro doing it anyway. Her story arc is a "coming-of-age" tale, and it's told pretty realistically.
Secondly, the absence of good role models. Aiko is a good role model, as I just explained, and so is her male counterpart Kanzaki. He finds a way to stop the Malignant Matter and since he alone can stop the horrors it will wreak upon the world, he puts everything on the line for the greater good. No spoilers, but his final arc in the last couple of episodes really is the icing on a very noble cake.
Lastly, my contention with the violence rating should be justified, since there is little to no person-to person violence. The matter is a blob. Just... a bunch of gross matter in a pile. There is one human standoff, and some of the deaths of a few characters and extras at the hands of the Matter is somewhat disturbing. I'll say that at a minimum.
Really, if there's any reason that a kid shouldn't watch this show, it's because of the Matter itself. Some of the characters interactions with it, especially towards the end (again, no spoilers), are a little disturbing, offputting, and made me, a grown man, uncomfortable.
All in all, it breaks a few anime troipes and cliches, and should be applauded for that. I have no problem recommending this as a-okay for kids 13+, granted that the parent(s) has/have taught thier kids the difference between fiction and reality and are sure their kids are mature enough to handle some tough life questions.