Back into the box
First Mentioned: WB2014 Duke Forecastle - Part 10
According to the Book of Canon, Titans judge units after they croak. Most units are found to have lived an acceptable life but not an extraordinary one, Scripture has several descriptions to what happens to these units, such as “rejoining the spirit of the world,” “returning to zero,” and “going back into the box.”
It is understood to mean that the unit will lose it's identity and melt away, perhaps with a deep and lingering (or even eternal) sense of satisfaction.
Real World References
Game pieces are put back in the box after the game is finished.