He was originally a member of the Order of the Moonlight Horse assassination organization. In S.1194, when Harwood would have been 33, the Order was destroyed by Ouroboros's most powerful agents. Alongside fellow members of the now-destroyed Order, Lucrezia Isselee and Sharon Kreuger, Oathbreaker later joined Ouroboros. He became the Fourth Anguis of the society.
Before Kuro no Kiseki
In Trails in the Sky the 3rd, Star Door 14: "Phantasmal Blaze", Harwood expresses his surprise over Georg Weissmann's death following the conclusion Gospel Plan and inquires after the assassin's name. He then criticises the Second Anguis for "not even [mourning Leonhardt's] loss for more than a second before setting [her] eyes on a new guy".
Information about Harwood before Kuro no Kiseki was limited. He was only known as (Thousand) Oathbreaker. He may have been active in Erebonia during Trails of Cold Steel I and II,[Note 1]. He took on the Septian Church in Arteria alongside Mariabell Crois to prevent their interference in the Empire by the time of Trails of Cold Steel III.
- The alias Thousand Oathbreaker literally translates as 'one who has broken a thousand commandments'.
- Harwood's dialogue lines are written in a distinctive style in Japanese. His vowels are lengthened playfully as "なァ" or "ねェ", a trait he shares with Lechter Arundel.
- His voice actor in Trails in the Sky the 3rd Evolution, Keisuke Baba, also voiced Carl Regnitz in Trails of Cold Steel I, II, III, and IV and Dogi in Ys Seven.
- It's not known what is the cause of his ability to surround himself in dark aura and call shadow creatures.
- Ellroy Harwood might have willingly betrayed the Order for Ouroboros, as shown by his title and by the fact that Ouroboros' main tenet is that people have to join by their free will, and cannot be coerced to it.
- When Arianrhod enters the Celestial Globe in Trails to Azure, Chapter 3: "Budding Turmoil", she updates the other Anguis that "the rest will be left to Oathbreaker"[JP 1] before turning her attention to Crossbell. When she herself starts her activities in Erebonia from Trails of Cold Steel III, Chapter 3: "Pulse of Steel" onward, she states that "Oathbreaker and Mariabell have taken on the responsibility for Arteria".[JP 2]