The chances seem to be between 1 and 0.1%.

This means that if you were to open 100-1000 packs (depending on the actual chance), you would have a bit over 60% chance of having opened him.

NEVER go for jackpot ninja, the chances are so ridiculously small that you will probably never get it. The only event that seems to be a bit better than most is the SPENDING slot machine, there you will still need around 100-200 spins to get the jackpot ninja anyways.

If you really want hashirama, use seal scrolls or directly save coupons for when it appears in treasure of the sage or other events (he goeas at ~16k).

On a side note, we have asked time and time again for the odds of the treasures. We have never had a response. This combines with Oasis track record has made many believe that they actually cheat with the odds. Unfortunately we have no proof of either them doing things right or cheating, so speculation and resentment only grows in the community.