How to Defeat the Stormbringer
You will hunt this Gigant during the sub-quest Seaside Tornadoes.
This flying enemy is weak to earth and has a spirit core on its wing. Target that with earth artes for extra damage.
It also tends to fire tornadoes close to itself. For this reason, Shionne and Rinwell can both deal damage without getting hit too much, as long as either Law or Alphen can draw its attention. You can replace Law with Dohalim if you like since his primary element is earth. However, Law is definitely better for chaining big combos.
As Alphen use Destruction to hit the Gigant while it is airborne then use Shionne’s boost attack to knock it down. Spam Eternal Devastation while the Gigant is on the ground. Alphen’s boost attack can also down targets so don’t forget to use that too.
Once the enemy enters overlimit, it releases several massive tornadoes that can be easily dodged by sticking to the edge of the field. Continue attacking only after the beast has calmed down.