bouncing breasts
乳揺れ 荒ぶるおっぱい アニぱい 乳揺れ(うごイラ) 乳分身 あばれる乳
The female breasts, often medium breasts or large breasts, that are bouncing up and down in motion, usually in an animation. Thus it is different from shaking breasts left and right intentionally/deliberately in motion. If it is not an animation, something like a motion blur or motion lines must be present to convey a sense of movement.
If the breasts are bouncing in opposite directions, add the unaligned breasts tag as well.
Examples
See also
This tag implicates breasts (learn more).