Add, Logos React Replica (ロゴスリアクト・レプリカ, Rogosu Riakuto Repurika?), was created by Morgan le Fay as a seal for Rhongomyniad sometime after Artoria Pendragon's death. Its main purpose was to preserve mystery. It was a replica of Logos React, one of the Seven Superweapons of Atlas. Its pseudo-personality was modeled after Kay of the Knights of the Round Table.
Add is stored in a bird cage.