Play 溯回青空 on PC Play 溯回青空 on PC and Mac

About the Game

Humanity has reached its ninth chapter. After eight successive extinctions, people have opened what is known as the Ninth Orbit Human History, only to face a new and terrifying threat: the gods have launched the Orbit Correction Plan, a calculated effort to erase all traces of human existence from the timeline entirely. Back to the Blue Sky, the Japanese-style card RPG from PLANET X LIMITED, drops players into this high-stakes conflict as the one figure capable of turning the tide. The catch is that saving humanity requires becoming its darkest symbol. You are the Demon King.
The cast of knights you assemble is one of the game's strongest assets. These are not generic soldiers or interchangeable units. Each knight is a survivor from one of the eight previous human orbits, carrying distinct personalities, histories, and fighting styles that reflect the era they came from. Sword Edge Light, born from the glorious first orbit, carries the weight of a warrior civilization on his shoulders. Thousand Purple, the mysterious witch of the second orbit, brings an air of arcane unpredictability. Zero Shot Orange, the energetic boy of the eighth orbit, injects youthful energy into a roster that might otherwise feel defined purely by tragedy. What makes the character writing notable is how the game threads genuine emotional bonds, called fetters, between the player and each knight, turning the roster into something that feels personal rather than mechanical.
In battle, the game commits fully to spectacle. Key features of the combat system include:
Elaborate animated text effects that appear on screen during special moves, turning each ability into a visual event
Fully voiced characters who shout the names of their attacks, adding theatrical energy to every encounter
Q-version character animations that give the cast a distinct stylized charm without sacrificing expressiveness
A card-based structure that rewards thoughtful deck construction and strategic timing
Outside of combat, Back to the Blue Sky offers a base management experience centered on Garden, humanity's last sanctuary, described as a mysterious stronghold drifting through the blue sky. This is not just a hub menu dressed up with flavor text. Players can actively manage a ramen shop, tend to a library, and study records of human history through past orbits. These daily activities serve a thematic purpose: they represent the living culture that the knights are fighting to protect. The contrast between the warmth of Garden life and the bleakness of the doomsday conflict is intentional and forms a core part of the game's emotional identity.
That identity is built on what the developers describe as a cold-exterior, hot-core artistic philosophy. The visual and narrative tone wraps intense emotional stakes inside a restrained, melancholic surface aesthetic. The world is gray and grim at a glance, but underneath that surface runs a current of passionate investment in human survival and connection. Players who look beyond the doomsday framing will find a story built around blue skies and summer evenings as much as it is about war and extinction.
The game also contains a significant amount of hidden world-building. A Term Dictionary and Setting Database are available in-game at any point, allowing players to explore the enormous lore structure without being overwhelmed by mandatory exposition. The writing trusts players to follow their curiosity rather than forcing every detail into the main narrative flow.
Playing Back to the Blue Sky through MuMuPlayer on PC enhances virtually every layer of the experience. The animated combat effects and voice performances land with far more impact on a full-sized monitor, and mouse-based navigation makes managing the Garden base and building card decks significantly more comfortable. The stable performance environment that MuMuPlayer provides also ensures the voice-heavy, animation-rich battles play out without interruption, keeping the game's carefully crafted atmosphere intact from the first orbit to the last.