Scientifically speaking everything is wrong in this video. It seems like this guy is tryin to mimic the movements of breasts of that anime girl but that guy surely has not succeed.

Judging by the size of the anime girls breasts the centre of mass of the breast must be located near her nipples(assuming that her breasts are perfectly hemispherical) and let’s not forget the radius of the anime girls breasts. I think it might be 7-8 cm amd let’s consider its weight to be 1kg. Therefore moment of inertia of the breast will be equal to MR² (assuming the radius to be equal to radius of gyration)

Also 8cm =0.08m Therefore MOI= 1×(0.08)²=0.0064kg.m

But that’s not the case with balloons as they are light and they have large radius of gyration making its MOI larger as compared to the breasts of that anime girl which inturn will increase its angular momentum.

So, in terms of science this guy as failed miserably in mimicking the movements of breasts of this anime girl