Yes, typically the game is considered complete when you finish the story of any character.
In most cases, when you wrap up the story of any one character in Octopath Traveler, it marks the end. But it depends on how you define the 'end' - there might still be side quests or additional content to explore.
Chapter 450, ", Death of the Ashen Dead", is the clearest early answer because the violence around Anconi becomes final instead of hypothetical. It opens with That's really pitiful, why not come and worship the Blood God! and closes on A regular Powered Armor under an Interstellar Warrior, with a gap....
Chapter 112, "The Orchid Quest II", is the clearest early answer because it turns Bloody Green Orchids's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Damien knelt by the fallen Empyrean Bears, his blade flashing as he... and follows through with Stay close," he said, his voice low..
Chapter 421, ", Supreme Command?", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. A useful checkpoint is the way the scene starts with When Gu Hang first proposed to take the initiative to attack, I... and follows through with As the scattered Green Skin Ships fled in all directions, it was....
Chapter 436, ", Seven Horses Submit", is the clearest early answer because it turns Planetary Government's situation into a concrete plot event. It opens with This is a reasonable perception within the Empire, with not a single... and closes on The political systems there have completed their reforms, and the....
Chapter 22, "Sub-Skill Unlocked", is the clearest early answer because the violence around Gerald becomes final instead of hypothetical. The chapter turns that into something concrete by moving from You do not want to get eaten like…" Gerald paused his words,... to I can't move." Gerald confessed and Jack could only facepalm himself....
Chapter 429, ", Battle Moon", is the clearest early answer because the buildup finally cashes out in a real clash. It opens with The Planetary Defense Force of Frost Origin IV had been consolidated;... and closes on They had tried their hardest, but the real differences made the.... The key payoff is that the danger stops being abstract and the conflict around power growth becomes immediate, forcing the surrounding cast to react under pressure.
Chapter 436, ", Seven Horses Return to Allegiance", is the clearest early answer because it pushes Cultivating Horse into a new phase or setting. The chapter gives readers a real answer by opening on The number of inspector officers assigned to each planet is not... and ending on The reason for this is because there's a shipyard on the starport of....
Chapter 475, ", Let's First Get Past Mr. Gu", is the clearest early answer because it turns Green Skins's situation into a concrete plot event. The chapter turns that into something concrete by moving from The atmosphere between Erso and Gu Hang suddenly fell silent after... to They possessed their own mother planet, whose outputs all belonged to....
Chapter 67, "Gold Ranked!", is the clearest early answer because it turns Damien's situation into a concrete plot event. It opens with «-3,000 units of Magic Essence!» Damien smiled, understanding that... and closes on I don't want to have to resort to punishing you all with the (Pact of.... The key payoff is that the chapter closes with He was now Gold Ranked!, which gives power growth a stronger narrative position and pushes the relationship tension onward.
Chapter 456, ", The War Situation Changes Drastically", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter turns that into something concrete by moving from Both sides had learned their lessons, and the entire battlefield... to After all, the premise for these star sectors and planets ceding....