Muchuu no Tou

Based on the erotic doujin game by Shiganai Atelier (シガナイアトリエ).

The four suns that bestow blessings upon the world. When one of them vanished, the people mourned deeply. Naia, an aerial explorer who ventures across the skies, and Mano, an automaton, set out to investigate the Tower in the Mist—the place where the sun was said to have fallen—but they were caught in a storm, and their airship malfunctioned. While repairing it inside the tower, they decided to search for the sun.

“Well then, I’m off to investigate right away!”

However, the interior of the tower was an eerie space—a complex labyrinth teeming with countless monsters. To make matters worse, a ghost appeared, and Naia was captured. The ghost was controlled by Mary, a girl with a mysterious past. Though she seems somewhat carefree, she appears to show absolutely no mercy to intruders in the tower…

A tanned, energetic girl raised in the tropics and a fair-skinned, soft-skinned automaton (mechanical doll). The erotic adventure drama woven by this black-and-white, mismatched duo is about to begin!!

(Source: Getchu, translated)