Muchuu no Tou

Naia, an energetic aerial explorer raised in the tropics, and Mano, a fair-skinned automaton, travel the skies in their airship. When one of the four suns that bless the world vanishes, they set out to investigate the Tower in the Mist, where the sun is said to have fallen.

Caught in a storm, their airship malfunctions, forcing them to land inside the tower. The interior proves to be a eerie labyrinth teeming with monsters. Naia is captured by a ghost controlled by Mary, a girl with a mysterious past who shows no mercy to intruders. The mismatched duo must navigate the tower's dangers and uncover the truth behind the missing sun.