Nagi, a high school student adrift in the real world, navigates life with a lingering detachment from her environment. Her sound-color synesthesia paints reality in hues others cannot see, deepening her isolation. The unexplained disappearance of her mother—a manga artist who left behind cryptic illustrations of Upananta, a realm haunting Nagi’s dreams—hints at a hidden bond between them and the fantastical world.

Upananta’s floating islands and dragon riders fill Nagi’s recurring visions, growing vivid during fainting spells where she meets Thaim, a dragon rider desperate to save his crumbling homeland. When Thaim and his dragon materialize in her reality, Nagi embarks on a mission to find Akuta, a vanished hero central to averting dual-world collapse.

Guided by newfound artistic talents echoing her mother’s, Nagi deciphers Upananta’s myths, uncovering ties between her family’s past and the realm’s peril. Clues suggest her mother may have shaped or accessed Upananta itself. Teaming with Thaim, Akuta, and allies such as her friend Mame, Nagi battles foes endangering both worlds while confronting their accelerating convergence.

Her journey forces a reckoning between her self-perceived alienation and Upananta’s profound stakes. As truths about her mother’s fate and her own cross-dimensional influence emerge, Nagi evolves into a mediator straddling realities, wielding her synesthetic gifts and inherited legacy to mend fractures threatening existence itself.