For Remilia, most of her life was spent acting as a loyal subordinate to someone she hated the most. Her hate stemmed not from her loyalty to Illiana but something personal.
When she was still a young girl and someone who had just started treading her own Pathway that would one day lead her to become the Blade Monarch, her small tribe was personally massacred by Zaraya. She only survived by playing dead and burying herself by the dead bodies of the other tribe members.
Zaraya now had no recollection of that incident, just one of the smaller tribes or Dark World denizens he trampled on his way to becoming a Great One.
She then found her way into Illiana's tribe before the woman rose to become a Great One like Zaraya.
Remilia distinguished herself as a master of blades. Even her Spirit Pathway became somewhat unique as it aided her way to becoming a young Blade Master.