Hello, I tried to use the Homura model edited by J&J (http://tstorage.info/skfmtglwxrfu) but the physics of breast is totally crazy. Did I miss something or the model is bugged?
Crazy in what way? There are breast sliders to change how they bounce.
If you open in MMD, in the "Other" tab, the options are the 6,7,8th ones. The 8th one will make them less bouncy and that may be what you're looking for.
Done, but still bounces too much :(