This is the beginning — there is no prior arc. Arc 1 opens on the morning Red, Blue, and Leaf receive their starters in Pallet Town and sets the three of them on the road north toward Viridian and beyond.
Arc 1 is the origin in every sense: the morning Red Verres leaves Pallet Town, the forming of the trio who will carry the story, and the first hard lessons of a world where children are sent out among monsters. Red — pulled from school to apprentice under Professor Oak, bound for a Researcher's license and ultimately a lab devoted to the origin of every pokemon species — sets out with his oldest friend and rival Blue Oak, who means to be no figurehead but a true Champion, and Leaf Juniper, a Unovan professor's granddaughter chasing a book of regional legends and a path of her own. Across roughly a week they travel north from Pallet through Viridian City and into Viridian Forest toward Pewter, and by the arc's end they are battered, blooded, and changed — Red with a broken arm, all three having watched people and pokemon die.
The arc's spine is Red's running deconstruction of his world. He treats the universal "type" system as a meme — popular because it flatters human appetites, not because it carves reality at the joints — and begins sorting types into "substantive" and "descriptive," snagging productively on the places it refuses to make sense. Chapter by chapter he names and wields the tools of clear thinking: the scientific method (the charmander-oil experiment), correlation versus causation, sample bias, optimism bias and the planning fallacy, the availability heuristic, theory-induced blindness, false dichotomies, risk as magnitude × probability, and an ethics of personhood, information asymmetry, and tradeoffs. Beneath the techniques sit the mysteries that will drive the series: the Speciation Paradox — there are no psychic rattata, no species with only some psychic members, yet humans vary wildly in psychic and "dark" power — Red's own unnerving vulnerability to a mental attack, and the unexplained 37% "Other" anomaly in his spinarak.
Just as important is the emotional education the techniques can't supply. The trio hardens into something like family, and the world answers with death: the trainer Luke Koyama, dead in a beedrill field while they correctly, agonizingly choose not to act; a string of pokemon killed in the night's chaos. Blue is revealed as a dark mind, immune to psychic attack and long ashamed of it, and the strain nearly breaks the friendship when Red treats him as an experiment — one of several moments the arc uses to expose the shadow side of Red's and Blue's brilliance, the way instrumental genius can reach for a friend, or a dying shiftry, as a thing to be used. By the climax the three philosophies stand starkly apart: Blue butchering a pokemon alive to keep it, Leaf risking a shock to save one, Red analyzing it all from the ground with a shattered arm.
Around the children, the interludes open a far larger and darker picture. Red's mother Laura returns to journalism just as Professor Oak confides his fear that scientists across every region — including his lost friend Dr. Fuji — have been vanishing for a decade, perhaps taken by some organization operating between regions. In Fuchsia, Leader Koga's daughter Janine wages a poisoned, lethal vigilante war on Silph-linked corruption, and her father dismantles her certainty that a single hidden hand is behind it. And the Viridian Forest disaster itself — an electric rampage, a fire, an improbable glut of shiftry, a dead trainer whose pokemon simply vanished — keeps stacking misfortunes that individually look like bad luck and together look like too much coincidence. No one yet connects the threads; the arc's quiet achievement is to lay them where a careful reader will feel the itch.
It closes on Leader Brock — "stone endures" — riding the colossal onix he captured from Mount Moon to lead Pewter's rescue, instilling courage in the broken and surviving his own shiftry ambush before pointing the survivors toward his city. The trio enters Pewter alive, less innocent, and already carrying the questions the rest of the story will try to answer.