Enemies will aim at the control character, so you can predict the moves they will use at a distance from you.
Since auto characters have a high level of guard performance, I recommend taking advantage of this mechanism to take turns in the fight.
・When it's just around the corner.→Tail Whip or Gyre Spume
They mainly use it when Cloud or Tifa is attacking at close quarters.
As soon as this technique name appears on the Leviathan's HP gauge, switch to Aerith and then immediately turn to attack.
Cloud and Tifa will have a high chance of guarding you.
・When you're far away.→Briny Bellow or Briny Barrage
It's mainly used when Aeris is attacking from a distance.
As soon as this technique name appears on the Leviathan's HP gauge, immediately switch to Cloud or Tifa, then immediately turn to attack.
Aerith will have a high chance of guarding this one as well.
・Spinning Dive
Let's switch operations to the cloud. They will charge twice from the outer perimeter, but you can deal damage in one go by setting up a Conterstance!(Counter blow are not allowed.)
Make sure you have two ATBs in the cloud before this comes along.
It's easy to understand the movement before the assault, so I think a Conterstance can be successful right away.
・It's easy to get into Pressure state
With a high magic power Aerith, Arcane Ward -> Thundaga can immediately put you in a HEAT state.
Try to defeat it before it goes into flight mode.
Ideally, you should be able to defeat it after one stagger, or reduce it to 5% of your remaining HP.
While in flight mode, the tornado will follow the controlled character.
Target the main body of Leviathan with Thunder in the order in which the ATB has accumulated.