The Last Vanguard

In the year 3918 AD, the scientist now hailed as the "Father of Dimensional Space Theory" but at the time dismissed as a "madman," Dr. Max Payne, confirmed the theoretical foundation of "Dimensional Parallelism" and proposed the existence of "parallel spaces." However, this idea did not gain widespread acceptance at the time. It wasn't until fifty-five years later, in the year 3973, through the perseverance of Dr. Max Payne's successors, that the first parallel space was discovered, prompting humanity to gradually acknowledge the feasibility of "dimensional space theory" and the infinite possibilities of expanding human space. By the bicentennial of Dr. Max Payne's "Dimensional Space Theory," humanity had explored far and wide, discovering a total of six alternate dimensional spaces harboring life. Sticking to anthropocentric naming conventions, humans referred to their own inhabited space as the First Space, with the others named sequentially by their discovery—the Second Space, Third Space, and so forth, up to the Seventh Space. The Second Space, strictly speaking, is not a complete space. Initially discovered by the Sigler Nakamihara Space Research Center, it was not recognized as a dimensional space but rather believed to be a fault existing between two spaces. This is because the Second Space is a flat space. Unlike the First Space, where humans reside, composed of burning stars, orbiting planets and satellites, interstellar asteroids, and nebulae forming galaxies within an expansive universe, the Second Space is one of unimaginable existence, with only front and back, left and right, and no up or down. Though the nearest up or down distance might be billions of kilometers, these are trivial compared to the immeasurable depths of the universe. It was eventually recognized as a dimensional space due to its striking similarities with Earth's environment: vast landscapes stretching into eternity, to infinity. It has mountains, rivers, and lakes, along with changing weather patterns, albeit vastly different from Earth. The sky lacks the sun, moon, and stars, yet the radiant energy hues of rainbow-like crystalline brilliance illuminate the land. The most astonishing aspect of this space is its abundance of life forms, dramatically similar to Earth's, with discernible distinctions between flora and fauna. However, due to the space's uniqueness, its life forms possess extraordinary abilities. Some are incredibly powerful, able to withstand advanced weaponry. Three years after discovering the Second Space, explorers from humanity mapped, in exacting coordinates, a vast agglomeration of intelligent life forms 1.67 billion kilometers southeast of the entrance. Sixteen such settlements were uncovered, each with societal structures of intelligent life forms. Although less dense than Earth's population, these settlements cover a vast 60 billion square kilometers, housing over four billion individuals of various species combined. Religious adherents perceive the Second Space as akin to the fabled paradise where deities reside. Hence, it is popularly referred to as the Celestial Realm. In 3998, the "Secondary Dimensional Space Protection Act," colloquially known as the "Celestial Law," was passed by the Space Management Bureau, prohibiting any disturbance of the Celestial Realm's native inhabitants or revealing humans as interdimensional outsiders to them. The Third Space is the most incomprehensible to humanity, as it fundamentally lacks "time." Extensive research reveals that this space supports life, albeit in forms beyond human comprehension. The lives here exist on a different plane, rendering effective communication with human life impossible. This unique trait earned the Third Space its title—the Chaotic Dimension, remaining the least understood dimensional space by humanity. The Fourth Space delivered humanity its harshest lessons. It exists similarly to the First Space but with alien life forms markedly different from those in the First Space. At the Fourth Space's entrance star system, housing 88 planets, nearly every celestial body teems with life demonstrating astonishing robustness. These beings possess incomprehensible powers, with exceptional individuals capable of navigating space effortlessly, journeying between planets unaided. Despite lacking structured societal systems, they remain in tribal formations. Upon initial exploration, aggressive entities attacked the human team with xenophobic ferocity, leading to complete annihilation. Subsequent invasions through breached portals into the First Space inflicted severe human losses. Without discovering the Fifth Space, subsequent attacks from the Fourth Space might have led to humanity's extinction from their greatest discovery. Referred to ominously as the "Demon Realm," the Fourth Space entrance remains heavily fortified against incursions by these powerful beings. The Fifth Space marks an anomaly among numerous discovered dimensions. Unlike typical spaces marked by life signs, the Fifth lacks life yet harbors relics of an advanced civilization. Research indicates a previously thriving, highly advanced civilization once existed, possibly succumbing to a peak-and-decline cycle, war, or unguessable disasters causing its complete extinction. Current explorations suggest this civilization once commanded an expansive empire based from its home star, spanning tens of star systems. This discovery radically informs the present understanding of advanced technology, having developed over a billion years ahead of humanity's current standing. The technological legacy from this ancient civilization significantly bolstered human technological prowess in a short span, enabling militaristic fortification to repel repeated incursions from the "Demon Realm." Leveraging these ancient remnants helped humanity develop its technologies, catapulting its historical progress forward. Colloquially dubbed the "Realm of the Future," some call it the "Phantom Realm." The Sixth and Seventh Spaces were discovered in tandem, though the Seventh was not directly found by humans. When the Sixth was identified, another portal to the Seventh Space was detected within it. Life in the Sixth Space exists at a development stage akin to humanity’s primitive era. Meanwhile, the Seventh Space's civilization had advanced slightly faster than humanity, establishing contact with the Sixth Space millennia ago, spurring its evolution yet striving to minimize interference. The seventh space, where humans have never been.