What happens in the Coalition Invasion arc?
The Coalition Invasion arc begins when Riboku of Zhao, the manga's great strategist, assembles an alliance of Zhao, Chu, Wei, Han and Yan to erase Qin before it grows too strong. It is the first time Kingdom operates at full continental scale, with separate armies converging on Qin's great border fortress at Kankoku Pass.
Hara structures the arc as interlocking fronts. Each Qin general holds a section of the pass against a different enemy commander, and the chapters cut between duels, sieges and cavalry clashes that all share one clock. The device became the series' template for every later mega battle.
When Chu's army breaks through and marches on the capital, the arc narrows to the defense of Sai, a small city where Ei Sei himself takes the field with a militia of citizens. The king fighting in the streets is one of the most famous sequences in the manga and a centerpiece of the anime's third season and the live action films' later entries.
The arc also deepens the series' politics. Qin survives, but the coalition's existence proves Ei Sei's point and his enemies' fear at the same time: unification is now openly the question of the age, argued by generals as much as by kings.
In tankobon terms the arc spans a run of volumes in the high teens to low twenties of the Japanese edition, a stretch many collectors treat as the essential early shelf, since it contains the first appearances and deaths that the rest of the series keeps referencing.
