How to Defeat the Boisterous Roper
You will be hunting this one during the sub-quest Opening Up Trade. But you can also kill it much sooner when you go through the Ulvhan Grotto for the first time.
This Gigant roams the center of the Ulvhan Grotto and is accompanied two Ropers in battle. All enemies are weak to wind. As Alphen, use wind artes such as Orochi’s Galeforce Fury or Severing Wind to rack up some good damage. The Gigant’s arms have impressive reach however, so keep watch while fighting up close. Leaving Shionne on Auto is fine so long as you set her to “fight in moderation”.
A wind arte counter after a perfect evade also does wonders here; try that once you figure out the timing for the arms. As for the Gigant’s attacks, it has Stalagmite which is an AoE earth arte that hits the spot directly below the character you’re controlling. Move away and it should miss completely.
The Boisterous Reaper also expels green sludge that can poison anyone it hits on top of some serious damage. Simply avoid stepping on the stuff and you’re good. Finally, when the monster plant turns blue, it is more likely to do a desperation attack. The battle area will flash red when it’s about to do this, so abandon any ongoing offense and evade hard.