According to this topic over at Capcom-Unity, there is an undiscovered Rockman 9 secret which may in fact be a secret weapon.
Taking a gander at the Rockman 9 tile set, Tornado Man noticed a peculiar "throwing" animation for both Rockman and Blues (pictured). This animation is not in the game, which has led many to believe it belongs to a secret weapon of sorts.
Actually, if you'll notice, the pause screen contains a vacant spot for a potential twelfth weapon. Hmm....
We'll see how this one plays out. Stay tuned!