Across the Sun invokes a metaphysical journey. Four adopted young adults flee an invasion and are magically displaced into a parallel world where they unknowingly disrupt a violent slave trade. Aeden, the eldest, is haunted by a strange dream. He is determined to protect his siblings and new comrades, and learns most of the world considers his divine magic to be evil. He rescues an enslaved woman, putting himself and his siblings in danger. Ruccharieu "Rook" is obsessed with water and hydraulic pressure. He is gifted at using arcane magic and craves knowledge. During a dangerous encounter, he learns someone has been occupying his body like a symbiote all along. Niwa loves to share stories with the summoned spirits of her deceased ancestors. As her abilities improve, she gains self-confidence, and later summons someone who knows the truth about what happened back home. Kliyd, the youngest, is a tikus (a humanoid rat person) who often has premonitions. After fleeing their home, she learns the tikus are the enslaved race of this parallel world. Stealthy and athletic, Kliyd hides her emotions, but is fiercely loyal to her family. The siblings are determined to stick together as they search for their missing parents, Gorram and Saba, hoping to be reunited soon.