This story is what I’d call a background building story. Tiaver, the main character of this story is not a significant character. He will show up randomly in stories, though.
Don't know where to begin?
While ultimately it doesn't matter which arc you begin with, Cecil arc is recommended if you want my recommendation.
And then Masu arc + Shattered union arc.
Feel free to visit the lore section as well which holds stories of its own.