Strength +25

Required pirate level: 65

Obtained by synthesizing 50 Shichiseiken Fragments and costs 18000 beli.

Shichiseiken Fragment can be obtained from Adventure mode normal or elite missions:
Chapter 9(Enies Lobby), mission 8(Robin Struggles).
Chapter 10(Thriller Bark), mission 8(Lightning Kick!).

NOTE: For this item, it is far easier to get it from Ordeals, because it spawns a LOT more often. However, you will need a crew level of 75 to enter difficulty 4.