Marble is the middle child of Foeslayer and Arctic. She was still born under 3 moons, just late midnight. She and Darkstalker became very close, and she was also the only one who understood Whiteout. She became the anchor holding the siblings together, in a way. As they grew up, Darkstalker would tell her about his visions of Clearsight and his future. She would listen and share visions of her own. He would tell her that, when he became queen, Marble and Whiteout would live in the palace, safe and far away from Artic. They became quite close. Darkstalker told Marble about his scroll first before Clearsight, and Marble got some mixed feelings about it. Skipping ahead when Darkstalker became . . . soulless I guess, she would try to talk sense into him. When Artic took Whiteout, Marble tried to fight him. He put a silencing charm on her and knocked her out. Darkstalker broke the spell, of course, and went after Artic, etc. Skipping ahead after the whole Arctic-death fiasco, Marble followed Clearsight to Pantala and became the savior of Patala along with her. She kept a diary of her life, and she never stopped loving Darkstalker, even after what he did.
Credit to Tui, songwriters, and web.