The Holy Grail War expands from a ritualistic duel into an actual battlefield, and that shift means servants stop being puzzle pieces in a mage's plan and start being soldiers who know they're expendable. Kairi and Mordred's partnership cuts deeper than the usual master-servant dynamic because neither one pretends to like the other, yet they become the only real thing in a war full of people lying about their intentions. Sieg might be a hollow protagonist, but that emptiness forces you to watch the war itself instead of following one character's journey through it.

Decades ago, during the chaos of World War II, a magus stole the Holy Grail, the sacred relic once fought over in Fuyuki. Now the Yggdmillennia family, which has taken the Grail as its emblem, announces that it holds the artifact and breaks away from the Mages' Association. The Association sends fifty elite magi to seize it, but an unknown Servant kills all of them except one, and that survivor returns carrying Yggdmillennia's declaration of war. With only two sides involved, the Holy Grail War changes shape: instead of a battle royale among seven pairs, each faction fields seven masters and seven Servants, and the side that loses all of its combatants first gives up the Grail. What unfolds is warfare on an unprecedented scale, as fourteen masters summon their legendary heroes and gather for the Great Holy Grail War.