Xasha chose Ryyju's Heaven Smiting Physique because it was the most versatile Body Tempering Art for his purposes. It had great applications in combat and Artificing; it is not the best at either but the best of both. He thought long and hard about giving up higher fighting ability in exchange for Artificing ability. He came to the conclusion that he wasn't a fighter; he wasn't just a fighter. Artifacts were as important to Falling Stardust's rise as anything else.
His role was to empower those around him to protect themselves and the people they care about and encourage those people to do the same. That is the ideal cycle rather than him thinking of himself as a savior chosen by the heavens, and only he can save the day. He laughed at himself for having such idiotic thoughts in the first place.
