Leviathan (Final Fantasy XV)

Leviathan, also known as the Hydraen, is an Astral who appears in Final Fantasy XV. She is one of the Six and a sea serpent who controls water. Noctis Lucis Caelum forges a pact with Leviathan after defeating her at Altissia.

Profile
Like the other Astrals, Leviathan is based on a recurring summon in the Final Fantasy series. She is a giant blue sea serpent, that also has multiple wing like appendages.

Story
Leviathan slumbers under the waters of Altissia, she is usually referred to as the "The Tide Mother" and looked upon with both great fear and respect

After the fall of Insomnia, Leviathan is awakened by Lunafreya Nox Fleuret, the Oracle. She asks him to lend his power to Noctis Lucis Caelum, unlike with Titan. The Hydraen takes great offense to being awaken by a mortal, stating that Noctis must earn her power.

During Leviathan's rampage in Altissia, Titan appears to combat the enraged Hydraean. His attack creates a massive tsunami that engulfs the upper city, as well as Noctis and Lunafreya.

Obtained
Noctis obtains Titan at the end of Chapter 9.

Battle
After acquiring Leviathan as a summon, she has a greater chance of appearing if the party is fighting near a body of water.. When summoned, Leviathan will Leviathan all enemies in the area with a massive tidal wave.

Boss
Leviathan is fought at the end of Chapter 9. Noctis must defeat her by first dodging her attacks in the first phase of the fight before finishing her off with Armiger.

Trivia

 * She was one of the first summons designed for the game, from when it was known as Final Fantasy Versus XIII.