I feel Arboras and Banila have never been used to best story potential
You have two entities who were sealed away, whose only goal is to kill eachother.
Ultraman: The Ultimate Hero (The American Ultraman that never played in the U.S) had a interesting idea, with Banila able to reform almost immediately after being melted by Arboras’s acid, implying both monsters have high regeneration that keeps them just fighting over and over.
But there is still more: why were they sealed away? How? How did this rivalry start?
I feel you could do something with arms races and mutual destruction like The Butter Battle Book by Dr.Seusse.
Or guardian monsters turned into war machines by human allies.
Perhaps they were sealed away as part of a long process to purify them of their anger/corruption, which could turn into a plotline other sealed monsters or finding a nonviolent solution.