Million Depth is a "deep-diving action strategy game" where Moma, a human girl from outer space, visits Earth to find her only friend, "you", and dives into the million-floor deep underground world known as Naraka Akasha.

As Moma, players will have to design and craft their own original weapons and engage in strategic time-freezing battles to survive the hostile environment of Naraka Akasha in order to reach the bottom and uncover the true identity of the mysterious "you".

To Moma, left drifting all alone in space, messaging her Earth friend "you" was the only thing that kept her going.
After all of her dearest crewmates died from a virus, the only thing to do was the daily aptitude test.
But as long as Moma could imagine the scenery of Earth as described by "you", she managed to live through the boredom and solitude of life on the ship.

"This will be my last message. I'm sorry. Thank you."

"You" never sent another message, but Moma knows where they are—a million-floor deep abyss known as Naraka Akasha, the only place on Earth fit for human survival.
Even though she has no idea what "you" looks like, Moma decides to dive into the underground world in search of her only friend...