I am really fascinated by Vanyel and Tantras too; that whole period between Pawn and Price when Vanyel was beginning to establish his reputation is so under utilized. But, I guess it's not surprising that they got close, because Tantras is the one who found Vanyel after he was Chosen and carried him back to the palace. Makes sense then that in canon Tantras takes on a sort of caretaker role, urging Van to rest, offering to do his paperwork, lending him uniforms, etc. He still remembers that before Vanyel was the exalted Herald Mage, he was a scared, sick, grieving kid.