Look this image that I uploaded. In it there are two images side by side, one is the bank background, another is Ruzena. If you notice, the two images are exactly the same size, but Ruzena's image has a transparent background.
Renpy has a function that allows only the "non-transparent" part of the image to be clickable. In this way, I can ovelay Ruzena's image to the background, and only the pixels that make up Ruzena are interactive. The rest of the image is ignored.
Renpy disables this feature on ports for Android because this kind of thing requires some processing power and mobile devices are generally not very fast.
So if I try to make a port from Solvalley or HS Tutor to Android, it will not work (it will be impossible to navigate through the maps). Apparently some guys know how to make it work on Android, since you could play the game normally. Unfortunately this is not something so trivial and probably requires a certain software knowledge that is beyond my capabilities.
For now, I'm hoping Renpy will allow the use of "focus_mask" on Android.