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
Breasts in motion, usually in an animation. If it is not an animation, something like a motion blur or motion lines must be present to convey a sense of movement.
If one breast is up and the other is down, add the unaligned breasts tag as well.