Impressive stuff. Just out of curiosity, that line that's on the bottom of the models right boob, is that just the way the shading happens to be reflecting? At first, I thought it was a mesh tear, but it on closer inspection, I think it's just some funky shadowing.

Thanks! The shiny material is a simple shader preset for the viewport. I think it's some rim light reflection.

Can you go a bit more in depth for this one? what bone constraints setup do you use? hpw are they weight painted? can jiggle physics be applied on such mechanism?

The breast is deformed by nine bones. One primary at the nipple and the others around it. These are attached to a circle spline around the breast that follows the movement of the primary bone and the chest. The diameter of the spline depends on the distance from the primary bone to the chest for simplified volume preservation.
There are jiggle physics with changeable behavior.
I hope that explains it all. English is not my main language.

yes! pretty much! thank you.
Tho kinda sad, that there is no easy export to game engines. 9 extra bones is kinda very heavy
but for renders animation its top tier quality