My Room refers to the private room given to each Master.
It is one of the few places where you can catch a break from the serious atmosphere of the Holy Grail War.
My Room is a completely private space, and anything that is discussed inside will never be leaked or overheard.
Moon Cell’s prime objective during the Holy Grail War is to observe and better understand humans, but only under special circumstances can Moon Cell record what’s happening inside.
By default it’s just a regular classroom, but depending on a Master’s codecast skills it can change in various ways.
The protagonist is unable to even change the interior design, but magus on the level of Leo or Rin can completely customize everything.
Cas-ko’s room in CCC is missing the Yes/No pillows and instead Agree/Disagree pillows have been unscrupulously implemented.