The attack Rein ended up preparing was mainly an ice element based attack but it was also getting a boost from his fire element. He also used his concept of cold to boost the power of the ice. With that he created a small ball of ice to throw it toward the tree. This ball might look small but inside it Rein had concentrated a vast amount of frost energy which was forcefully contented inside this ball area.
Rein was planning to destabilize that force by his fire element which would then create a large explosion. As the area of the explosion would be limited, the power generated by it would be massive. Rein was planning to destroy the plant horizontally instead of vertically as that way he needed to cover less area.
So after finding a perfect chance, he launched that small ball directly at the trunk of the tree where a weak point was present. Then Rein teleported out of the area to create some distance as he did not want to get caught in his own attack.
