Add, a sentient Mystic Code, serves as the alternate form of the Holy Spear Rhongomyniad. To preserve the spear’s mystery and lessen its burden on the wielder, he assumes a compact, cube-like shape, functioning as Gray’s primary weapon system.

Highly talkative and sarcastic, Add frequently offers commentary and displays distinct humor. His behavioral patterns and speech mannerisms reflect those of Sir Kay, King Arthur’s brother, stemming from Rhongomyniad’s ties to Arthurian legends.

In combat, Add transforms into versatile armaments for Gray. His primary scythe form deliberately distances itself from a spear’s appearance to further conceal Rhongomyniad’s nature. He adapts to other weapons like bows or shields as needed, while also providing observational insights during investigations.

Add’s existence binds him to Gray’s destiny. Created through her village’s efforts to forge a vessel for Artoria Pendragon’s legacy, he shares her connection to the Holy Spear. As Gray’s appearance gradually shifts to resemble Artoria’s due to wielding Rhongomyniad, Add remains her constant companion, observing and remarking on her struggles.

Within broader lore, particularly *Fate/Grand Order*, Add is formally classified as Gray’s Noble Phantasm due to her demi-servant status. This acknowledges his divine-construct origins while affirming his role as her primary armament. His sentient nature and independent conversational abilities persist across all appearances.