Add-Ons are enigmatic floating objects that assist their owner, thus bolstering their overall power. All of them are named after Greek letters. They act as if they are additional party members when acquired, in standard RPG fashion, even though their natures are not explained.
They can attack, use Competences, and be equipped with an assortment of equipment. The Batter can find them in every Zone except Zone 0. Each Add-On has its own unique set of competences that allows it to play a role in the party unique to the others. One might either be an offensive caster, a healer, or a buff caster. The Batter can collect up to three Add-Ons throughout the game. The only other Add-On user seen in the game is The Queen, who uses the entities in a very similar manner when she encounters The Batter in The Room.
The Batter's Add-Ons' class are "Father" (Alpha), "Son" (Omega) and "Holy Spirit" (Epsilon), which seem to allude to the Holy Trinity.
Due to this allusion, the Batter's seemingly religious demeanor and his Add-Ons' shared shape, they may be interpreted as the Batter's halos.
The Queen's own Add-Ons are much larger and uniquely intricate compared to the Batter's ones, which also visually fit with her elegant manner of dress.
Delta, Sigma, and Ipsilon are referred to as, "Royal Add-Ons".
There are other characters that seem to use things similar to Add-Ons but are not confirmed as actual Add-Ons:
Sugar uses four Add-On like battle companions known as Dummies, which are pieces of candy suspended on hooks on her hands. Like an Add-On, they are treated as if they are a separate party member and can cast competencies.
The Pastel Burnt has an Elsen's head as a kind of Add-On.
There are also characters that can summon in Add-On like party members during battle. Most notably they come in the form of speech bubbles though they seem to act as damage sponges rather than an actual attacker or caster. Examples of enemies that can do this are the Zone 1 guardian Dedan and fat spectres.