I’ve honestly been putting off answering this because, despite this being one of my top favorite League topics, it’s going to take more than one response to do!
The typecode system in Dream World is integral to its worldbuilding, and secondary to the story. However it’s rather complex so it’s still not 100% solidified. Nevertheless, here’s the basics as we currently have them:
In Dream World, there are 33 distinct “elements” of the world. These include natural things like fire, water, and shadow, as well as more ‘abstract’ things like daydreams, visions, and luck. 30 of these elements are natural, and 3 are rare “mutations.”
Every single inhabitant of the Dream World— which are collectively known as Jewel Monsters— resonates with at least two of these elements, and at most four.
Every element has its own symbol (here) and associated glyph (J, X, @, etc.) for the sake of shorthand identification.
So, when you use that shorthand to list which elements a certain monster resonates with— literally, when you group together the two to four symbols or glyphs applicable to them— that’s called a typecode!
Now to break down the typecode phenomenon in and of itself (this is where it gets tricky).
Each element within a typecode fits into one of four slots. Again, the first two are mandatory, and the second two are optional.
The FIRST slot is the biological element of a monster. It is called the CORE.
This element is determined by species, and so it is the most “physically obvious,” as It will also define that species’ basic abilities and physical characteristics. In other words, It is the element of the world that your form and instincts resonate with most, as a whole.
For example, a creature whose species is built for hot and dry environments will not be a Freeze (I) core; instead they will most likely be a Fire (F) or Molten (Z) core.
A core also has basic, “instinctive” effects on the personality, the way astrological star signs do for humans— to illustrate, no two Virgos will act exactly alike, but all Virgos commonly display some characteristics associated with the sign, in small or great amounts depending on the person. So, a coretype is helpful for a personality snapshot, but not a complex picture.
The SECOND slot is the secondary element of a monster. It is called the COMPLEMENT.
This element’s influence may or may not be reflected in one’s biology. Instead, it has a large influence on abilities, and it will affect the “way” the Core manifests or is expressed.
That’s a bit hard to explain in general; it’s very much an individualized thing. For example, if a Fire (F) core had a Psychic (M) complement, then they would use their M-associated mental deftness to complement their innate fiery traits and skills. The specifics of that is purely up to them, though!
This slot may also vary within a species, such as if there are major habitat differences (Kaiteo, Dionastra, etc.). When representing such a species as a whole, the variable complement will be called a switch slot, and it will be given a special symbol within the species typecode. (This does not occur in individual codes!)
The THIRD slot is tentatively the main ‘personality’ element of a monster. It is called the ACCENT.
(This one’s function is still foggy yet, so this isn’t official canon atm.)
It does not occur in all monsters, as it is not biologically linked. Instead, it is developed through personal quirks, tendencies, and partialities.
It can limitedly be harnessed in abilities but will not affect their biology.
Lastly, it is far more common for older or higher-morph monsters to have a third slot.
The FOURTH slot is the Jewel Form element of a monster. It is called the AFFINITY.
Very, very few monsters have Affinities, to the point where the 4th slot is commonly called a “bonus slot." Those that do have this slot filled are typically Guardians, Prophets, or Seers.
This is because this slot can only be filled through conscious effort and individual growth. It will not happen accidentally, by force, or before an individual is ready for it.
It is developed when a monster chooses and truly embodies their personal Virtue/Vice (an entire topic in itself). It represents that V/V in an elemental manner. This element’s qualities are what shine through in difficult situations— it is what allows one to overcome their biggest fears, doubts, and/or weaknesses.
Monsters with full typecodes can also achieve what is called a Jewel Power Form— a sort of “super mode” that can be temporarily achieved by sincerely tapping into the Affinity’s qualities. The Affinity then acts as a “double Core” while in a Jewel Power Form, granting an equally temporary but full embodiment of that element.
There are THREE BIG EXCEPTIONS to this set of rules, though.
The first exception applies to PROPHETS!
Prophet creatures are frequently born with COMPLETE TYPECODES. This is because the World has a specific job for them from the very beginning, one that is literally written into their very DNA.
However, having four full slots immediately upon being born is quite overwhelming, and depending on how it is handled, it can ultimately become either a great blessing or a great curse.
The second exception applies to THE JEWEL ELEMENTS!
These elements are unusual in that they do not naturally occur in a core slot— there is no species in existence with a Jewel Core. On the contrary, these two elements can spontaneously replace the species core in any individual at their birth. This typically only happens with Prophets, or with individuals chosen to be Guardians. This is because Jewel Cores have very powerful influences. The characteristics they bestow are strong to the point of overwhelming some, so individuals with Jewel elements in their typecodes can be emotionally unbalanced and/or unpredictable if they have not learned to manage these effects well.
Jewel elements can also spontaneously replace the 2nd or 3rd slot of an individual, which is less rare, and is often seen in Guardians. These function just like other types in those slots, although the characteristics they bestow are quite different of course.
Lastly, Jewel elements are probably the most commonly seen in 4th slots! This is because they are inherently tied to Jewel Power Forms.
The third exception applies to THE CORRUPTION ELEMENT!
Like the Jewel elements, no species has a Corruption Core. However, this element does not naturally occur at all.It is purely a mutation, occurring when a certain part of one’s personality becomes powerfully “corrupted”— in which case that corresponding element will be replaced by this one.
Corrupted Complements and Accents can be reversed, but this takes hard work on a personal level, to heal that part of the psyche
A corrupted Affinity is possible, but that would require a massive betrayal of the self, after reaching a point of growth where an affinity could be gained! Such a dramatic, self-sabotaging choice would take enormous effort and time to reverse… if it could be reversed at all.
Lastly, and perhaps most importantly:
There is no such thing as element dysphoria in the Dream World.
A Typecode is effectively determined by one’s soul, so the element whose qualities one resonates with most WILL be their Core!
Also, no typecode expressions are set in stone. They are very individualized! Two monsters can have identical typecodes and act very differently, as each can favor and express different traits and aspects of their personal resonant elements.
For example, one F-Core might favor the spitfiery side of their Core. Another F-Core may be warmer and more subdued. But both of them are expressing Fire traits, and they are both acting according to their own heart’s expression.
I’ll be making individual posts for each element in the near future, as it will be fun and informative. I hope this makes enough sense for now!
(And yes, Xenophon is widely assumed to have a Typecode because everyone thinks she’s a Jewel Monster. That’s entirely possible (and I will explain more of that phenomenon later too), but only time will tell!)