The tweet that inspired this artwork:

We noticed a funny. Usually GGST character files are 3 letter abbreviations, such as ABA, ANJ, etc. Couldn't find Jam. Strange. Should be just "JAM" right? NOPE! Her files are named USG for Usagi, her bunny.

Usagi is the main body, and Jam is simply its biomechanical extension

LightSolas said in comment #2592681:

The tweet that inspired this artwork:

Close enough, welcome back Haehyun.