When humans sleep or go outside……or otherwise aren’t noticing, they secretly move. They like customizing themselves by combining various parts, sometimes equipping weapons and armor and having fun battling like a sport. And when they notice a human, they return to being a model once again.

TL note: “They” is written as 模型[たち] (mokei-tachi, models), force-read as “カノジョ[たち]” (kanojo-tachi, they), with the exception of the last time once the humans return, in which it’s simply read as “model”.