Intro
Nagi no Asukara really seems to me like a crossover between Ponyo and Anohana because it's about some teengaers from the ocean and there is a lot of drama and romance in it. The sea and land are beautifully drawn and the relationships between characters are fun to watch grow.
There are these middle school students who must go to the school on the surface because the school in the sea was shut down. There is a city underwater known as Shishishio and a city by the sea on the surface known as Oshioshi (might want to check that though :P Edit: As of writing this review, I had not seen the show in the while and I had done it late a night. My apologies). If you need your romance/drama fix, look no further.
Story
There are two segments to Nagi no Asukara. The first segment introduces everyone and explores the differences between people who live underwater and then who live on the surface. This is where the main conflict in the first half arises. The second half happens five years after the events in the first arc happened and goes more in depth in the relationships that will blossom. I thought this was a brilliant move. As the first arc ends (with all of its chaos and things going on towards the end), you get excited to see what will happen next and the second arc feels like a whole new show or even a season 2.
This is a slice of life series but it has the element of romance so there will be lots of pairings going on. The pairs you think will get together around the middle of the series will change completely and I liked that because it was unexpected in a good way. You may not be happy with the final pairings (I wasn't, but it was still satisfying) but it's just one of those "too bad" things. There is a big love polygon going on throughout the show and it grows during the second half. In the second arc, I began to think differently about some characters so it was interesting to see how their character developed over time.
The story in the first arc may feel slow at first, but if you can stick with it, it will be quite rewarding.
Characters
The main cast includes five middle school students. First is Hikari, a hotheaded and short-tempered boy. As usual, he is a pretty annoying lead MC. Then there's Manaka, who is the really energetic crybaby. Kaname is the kind and nice guy and Chisaki is a tall and somewhat nervous girl. All of them possess a trait known as Ena. Ena is a thin film on the skin of people who live in the sea that lets them breathe underwater. If you stay on the surface too long, your Ena can dry up (so Hikari and his friends periodically soak in a pond near their school filled with salt water). Then they meet another boy named Tsumugu on the surface, who is often quiet and is just that one cool guy.
There are quite a few other side characters such as Hikari's sister, her daughter Miuna, Miuna's friend Sayu, and Hikari's father, who is the head priest of the town underwater. Then there is Uroko, who serves the Sea God (and often refers himself as a 'scale' of the Sea God). He watches over Shishishio. As the story progresses, it focuses the plot around these characters.
Character design is beautiful and the characters are able to create many new relationships during their time on the surface. Development of these characters is quite impressive as well.
Animation and Sound
NagiAsu, in my own opinion, is the best from P.A Works when it comes to animation. The beautiful sea scenes really make this show pop. The water is a nice blue and you can see schools of fish swimming by in the village underwater. The reflection of the sun adds for an impressive lighting effect. Life down under looks really relaxed. This really shines during the OP and ED sequences.
Personal Enjoyment
Being able to get to know so many characters and to be able to bond over time throughout the show is quite an experience. All of the romantic tension and slice of life aspects of this show make it a pleasure to watch. I really enjoyed it and if this is your preferred genre, you will too.
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Conlcusion__
Overall, Nagi no Asukara is a wonderful slice of life, drama, and romance series. It adds the element of the sea which I really liked. I don't have any complaints about this series at all (other than it's rather slow parts but this is nothing that should stop you from watching it). It's well done and the art is fabulous. The first arc might not be that interesting, but I say definitely stick around for the second one. This was probably my favorite anime of its season. If you've just finished Glasslip and you think P.A Works hasn't come out with a great show, think again.