its a reference to a in-game event about uni's transformation
Specifically, Uni's breasts actually shrink when she transforms. Nepgear thought she was padding.
When I'm next to her, I just lose all my self-confidence...I don't use pads!!!Big sis has got such a nice figure...Uni-chan, help me out!! Please lend me the padding you always wear!!Nepgear~, I've brought you some cake.It's just a lifting effect, honest*sigh*...