Book 3: Shadows of the Void

In the deepest recesses of the void, where time and space intertwined in chaotic patterns, Vaelros reflected on his origins. Long before he became the embodiment of darkness, he was a being of immense potential and light.
Based on the information provided, here's a brief summary for Book 3 of your fantasy series:

In this third installment of The Chronicles of Light and Darkness, Lyra Nightshade and her sister Elara join forces with their allies to defend the shining city of Lumina from the encroaching darkness of Vaelros. As the last bastion of hope for the land of Elarian, Lumina's fall would mean the triumph of shadow over light. The sisters must harness their strengths, uncover hidden powers, and rally their comrades in a desperate battle to save their home. With the fate of Lumina and Elarian hanging in the balance, Lyra and Elara's courage and unity will determine whether light can prevail against the looming threat of Vaelros.