Trap/Sissification
Since the game's universe consists of only females and futanaris, I don't think anything would technically be considered "Trap". However there are characters that will have a very similar body and anatomy type. Sissification is the same, it won't be to the letter, but there will be opportunities for you to make certain characters more "feminine" in regards to their personality and their physical features over time.
Attribute Theft
This is a genre/tag/fetish that isn't explored terribly often. There's actually a scene early in the game the describes how this works in universe.
Simple definition would be: altering one's physical appearance and/or attributes by taking and transferring them from another person--usually by means of another genre, such as
magic, fantasy, or shapeshifting. The "theft" of it is sometimes misleading, as it isn't always nonconsensual.
Random examples would be:
Non-Con: A dominant individual who is jealous of your height and stature, magically steals 6 inches of your height, rendering you 6 inches shorter, and them 6 inches taller.
Con: A submissive individual with a love of anal, offers you inches of their cock, decreasing their size and increasing yours, to increase the enjoyment for both of you.
Transformation
For this game, transformation will tie into the deeper fantasy elements of the world. The above attribute theft is underneath the transformation "umbrella". But there will be characters more "adept" and their abilties that will allow them to alter their appearance at will, akin to a shapeshifter. This could be anything from adding to their cup size, changing their skin tone, mimicking and "cloning" themselves into other characters, and eventually moving into more advanced stuff like demonic, beastial, and fantasy forms.
Hope that clears some stuff up!