Anime where genetically modified girls fight aliens/sea monsters

As per Anime about half-human girls who fight monsters?, this may be Black Bullet.

This anime aired in 2014, and was a one-cours series, lasting 13 episodes. It takes place in a world devastated by the "Gastrea" entities, and the characters who fight the Gastrea are divided into pairs of a "Promoter", who leads their partner in their battles, and an "Initiator", who is a "Cursed Child". The Cursed Children are young women whose bodies were altered by the effects of the Gastrea before they were born. Since the series takes place about ten years after the Gastrea appeared, the Cursed Children are all around ten years old.

Found with a search for anime girls fight sea monsters

The name of this anime is Freezing

The series revolves around the invasion of Earth by an interdimensional force called the Nova, and a special military group of genetically engineered young women called Pandoras. Pandoras fight alongside their male partners known as Limiters, who are created to combat the Nova. The story centers around Kazuya Aoi, a Limiter whose late sister was a Pandora, and Satellizer el Bridget, a Pandora with a cold personality who is known as the "Untouchable Queen" due to her intense aphephobia. Both are enrolled at West Genetics Academy, which is a training school for Pandoras and Limiters.