Strength training piano keyboard, unused item

Muscle Strengthening Piano Keys
Supervised by Yoshiko Kurokawa
For strengthening the first joint of the fingers
Includes instructions

I bought this with the intention of using it, but I ended up not having the opportunity and it has been stored at home for a long time. It is no longer sold, so I believe it is a rare item that is difficult to obtain. Although it is unused, due to long-term storage, there are areas that have yellowed and some mold. I believe it will not affect use, but please understand and thank you for your consideration.

For those whose first finger joint caves in
For those who cannot produce a wide range of sounds
For those who started piano as adults

Strengthens the first joint of the fingers
Greatly effective for strengthening the muscles of the palm!
For those whose first finger joint feels floppy
For those who cannot produce good sound
This is a product with immediate effects for such individuals!

Also useful for finger warm-ups before piano competitions or just before the actual performance.