When Marin and Urin – two sisters who live in the sea – find a ring that dropped into the water from the land of Sky, they decided to travel above to return it. There, amidst a bustling festival, they meet the ring’s owner; her name is Kanon, and she wants nothing to do with the ring, which was a present by her ex-boyfriend. After Kanon refuses to accept the ring and throws it away once more, the girls continue to search for it, accidentally releasing half of a great evil whose spirit was sealed both above and below the water. But luckily, there’s hope – Matsumoto, the Elder Turtle from the sea, appears and reveals that Marin is none other than the Priestess of the Sea, charged with defeating the villain. Marin must now fight alongside Kanon - who discovers she’s the Priestess of the Sky - to put a stop to this ancient power and its possessed minions before it’s too late…
Awayuki Himeno is a normal schoolgirl who is in a bind: her father’s remarriage yielded two new cruel stepsisters, and to top it off, she meets seven men who call themselves Liefe Knights. They reveal to her that she's a Pretear, someone who can lend powers to them when their powers aren’t enough to defeat the evil creatures called mayouchuu. Now, she has to fight the ambitious Fenrir, whose only purpose is to leech the life force from all living beings. Can Himeno save the world and find a way to deal with her growing feelings for one of the Liefe Knights?
Pretear and Umi Monogatari are similar in many ways, both of them feature a magical girl theme, both of them feature a female protagonist that gains superpowers aginst her will, both of them feature main protagonists assigned with a mission to seal an evil being/spirit helped by other side characters. Pretear and Umi Monogatari have many plot similarities and both have a similar feeling so if you like one then check up the other one as well.
While visiting his hometown, junior high school student Michishio Nagasumi's life was changed forever when he nearly drowned. Though he was saved by a mermaid named San, there’s a catch -- her family is part of a merfolk mafia, and they abide by a strict rule: If a mermaid is discovered by a man, either he or the mermaid must die. That is, unless the man marries into the family! Faced with such a decision, Nagasumi can only oblige their customs and become a "happy" newlywed. Now, with a new school year around the corner, Nagasumi must find a way to deal with his new bride, keep her true nature a secret, and most importantly, escape inevitable death at the hands of San's over-protective father’s gang!
Both anime are about girls that are able to survive underwater. Seto no Hanayome takes the mermaid / comedy approach where Umi Monogatari they are more just water dwellers naturally and takes things more seriously even though they are magical girls. Both shows have a similar feel to them even though Seto is more hyper than the other. This is kind of a gut recommendation cause i'm sure if you liked one you will enjoy the other.
Both shows take magical girls and put them in a slightly different setting than we are use to. The watery background in both shows is oddly soothing. Nothing much happens in either show but the graphics and music fit together very nicely.Campanella is a little more light hearted than Umi Monogatari. If you liked one give the other a try.