Theta

Sir Theta (シータ) is a posthumous character referenced in Silver NX.

Theta was an "Excalibur"-class elite warrior serving the then-king of England. In the early to mid 1200's, he was one of the few members of the Legendary Knights that did not turn corrupt, and was an ally to Epsilon during the Renegade Calamity.

Unfortunately, he was killed by the rampaging Omicron and over 800 years later, in 2034, Theta and the others' spirits called out to and guided Shunichi/Epsilon to the Twilight Note.

Personality
Theta was described as a kind, compassionate, and incredibly loyal man, likely due to his time with Rho and Epsilon.

One of his most notable traits was that of his unwavering selflessness, putting the well-being of others before his. In 2034, after 800 years of being trapped in secret, Theta is shown to have grown very frustrated, impatient, and angry; however, after looking into Shunichi's heart, Theta recognized him and reverted to his old personality.

Background
Growing up, Sir Theta trained in magic and sword fighting, becoming a knight and meeting Rho and Epsilon.

During the Renegade Calamity, he led a party in search for Epsilon when it was believed that he had perished, and upon finding him, Theta became one of his primary allies, helping in the hunt for the monsters created by the other Legendary Knights. Discovering that his teammates were corrupt, he set out to find them, taking part in Xi's duel with Rho in the palace before the two were knocked unconscious by Psi.

After awakening, Theta found Rho and his key missing, eventually discovering William's corpse in a pile of rubble. A few months later, Theta bore witness to the deaths of Iota, Rho, and Johnson by the rampaging Omicron, and although he fought valiantly, Theta himself eventually died pushing Epsilon out of the way of Omicron's white lightning bolt. His and the others' death gave Epsilon the resolve to defeat and kill the monster.

Twilight's Destiny Arc
Over the next 800 years, Theta's spirit remained hidden in England and was awakened with the arrival/return of Shunichi and his group.

Along with the spirits of Rho, Amara of Termina, Johnson, Iota, and William, Theta's spirit guided Shunichi to the location of the Twilight Note and his soul was to put rest following the deaths of Theodore Heinrich, and Upsilon.