Magma's mother's sister was King Basmu's mother, that making her related to King Drakon. Magma had two children, Dahlia and TBN. When Dahlia refused to marry who she was assigned to, and it was revealed that she was seeing a healer, Magma became so angry that she disowned her. According to the Starfell Clan's procedures, Dahlia was to be kicked out of the Clan, and shamed for her betrayal to the stars her entire life. But Magma was not pleased with that, she wanted her killed, and it was easy enough to get every member of the Clan to agree on that, since they all essentially hated Dahlia.
TBN, however, still cared for her sister so she went in secret to the king and implored him to make an order sparing her sister's life. As she was related to him, Drakon decided that helping her out would be beneficial to him - nothing assures loyalty to the king more than owing him something. She could never betray him if he would save Dahlia's life. So he forbade the Starfell Clan to kill Dahlia, saving her life.
The Starfell Clan doesn't know why he decided on such a thing, and they don't suspect anybody for it. All except Magma, she is convinced it was TBN's doing, and she despises her for it.
TBN can not show affection to her sister, for if someone would see her she would be suspected. That's why she acts with Dehlia as if she despises her, but when nobody is around she acts like before everything. Dehlia doesn't understand why that is, she doesn't know that her life was saved because of her sister.
