breast padding
Padding designed to fit inside a bra or other clothing to enhance the appearance of the breasts. Also known as falsies, jellies or bust enhancements.
Can refer to the breast pads themselves, other objects being used to pad the breasts, the action of padding the breasts even if the pads aren't visible, or the concept of padding the breasts even when they aren't being padded.
Touhou character Izayoi Sakuya is often the center of the breast padding joke, as her bust is larger in the fighting game spin-offs than in the original series.