I was getting the vibres this chapter, that he was teh commander of the Stargi. Well well well. That ending. I guess I was right.
So to summary, Iguessing hes the commander of the Stargi, one of the unit members is a female rogue/thief, that has this tiny girl as her disciple. Since he has stated shes the disciple of his acquaintance and she referred to onee-sama before the fight. I guess she called him master because hes the commander of her teacher. Thats what I can make sense of this.