Knightwind
Hopefully this sets up Satoshi later learning under Tsunade and/or Sakura. The effectiveness of the Ope Ope scales with how scientifically literate the user is, so knowledge of biology and anatomy will be helpful. And given some of Law's more advanced techniques, physics and chemistry may also come in handy. Forget Chibaku Tensei, if Satoshi can figure out how to use the Ope Ope to induce false vacuum decay in a localized area, that's a S-Rank Jutsu right there.