Arjuna was once a slave, in fact he was bought by the Temple of the One God at the slave market. His owner then ( one of the priestesses) treated him badly and Safia required him through cunning and trickery. He was ten. She was twelve.
Safia saw him from time to time around the temple, saw him practice battle-skills both magic and physical, skills that he'd seen and memorized with one glance. She asked the High Priestess to recommend him to be a soldier. The High Priestess took him to the Order of the Iron Hawk, an elite force of magic and battle-skills that protected the temple, the city and the Sultan. In that order.
But like Safia, he was not an official member. Though he took vows, his vows was made to Safia and not to the order or to the one God. As he once said to Safia, "God did not save me that day in the market, you did."
The High Priestess nurtured his gratitude for Safia because she wanted him to be her guard as she went on her so-called 'mission'. And she freed him to follow Safia around as she further her education in the palace to the very slums of Sihr. On their little trips, Safia had four guards, men from the Order of the Iron Hawk. As they grew older, the guards diminishes from four to one: Arjuna.
Safia hated the High Priestess a little for that. Because she didn't want a guard, she wanted a friend.
To Arjuna's surprise, his time as a slave helped him learn the skills of assassination. To be a slave was to not be seen and to not be heard, to always observe, detect and to anticipate. To always expect danger and pain coming from every side. And to always suspect everyone.
As he grew, as he trained, his self-worth slowly buildt, deeply rooted to his skills as an assassin, one that he had because of Safia. He feels deeply indebted to Safia but not because of reasons that she suspected and disliked but because of his own reasons. To him Safia was tribe, was family, she was everything that keeps him grounded in the world.
For an assassin he is not dark or broody or guilt-ridden (which of course makes him more twisted in a way), he is easy going and has a fair sense of humor. He is careful though with Safia, is very hesitant of going against her but does not tolerate her facing danger alone without him. He is very protective of Safia but does not mean he stops her from doing everything, he simply asks Safia to let him follow her as she does her business.
They have a very weird relationship, not quite friends, not quite siblings, it is a mix of both.
Safia might not take him seriously at times, but she doesn't deny that they have a connection, a bond of trust that she has with no other. She might be resentful of him at times, but it stems from her discomfort of having Arjuna so tightly bound to her by ties of obligation and duty. But if Arjuna feels at all bound, it is a binding that he welcomes, he had been, for all intents and purposes, adrift all this while. Safia gives him something that he never had; a home.