“The first anime animator to include a breast bounce was Yoshiyuki Sadamoto,” claims Oku.
However, no commenter was able to point out a specific anime episode or sequence that predates the Daicon IV bounce, so it’s probably safe to say that even if Sadamoto my not have animated anime’s first breast bounce, he animated the first one that people really remembered.
Regardless of the reason, though, mammary motion in anime is now common enough that a chest bounce hardly warrants an eyebrow raise-level of surprise.
But nothing happens in anime without someone drawing it, and manga artist Hiroya Oku (best known for Gantz), recently tweeted a claim as to who was the first anime animator to include a breast bounce in their work.