Holy War

The Holy War (聖戦, Seisen) is the main conflict the D.Gray-man series revolves around. Having begun more than 7000 years ago, this war opposes the Noah Family led by The Earl of Millennium and the wielders of Innocence who shall be led by the Wielder of the Heart. The events of the war are recorded by the Bookman Clan.

Trivia

 * "Seisen" is a word meaning war for justice, which is regarded as religiously sacred. In the christian context of the story, it is heavily referencing the crusades.