A Secret Plan to Defeat Buu! Its Name is Fusion (ブウを倒す秘策 その名はフュージョン！ Bū o Taosu Hisaku Sono Na wa Fyūjon!) is the one hundred twenty-ninth episode of Dragon Ball Z Kai. Its Japanese air date is September 21, 2014.
As Majin Buu destroys cities, Bulma and the others gather the Dragon Balls in order to resurrect the audience members killed by Vegeta. Learning that the last ball is on a solitary island in the middle of a lake, they rush there. After a difficult struggle, they steal the Dragon Ballz from the island monster that had it! Meanwhile, at God’s temple, having brought Goten and Trunks there, Piccolo and Krillin wrack their brains to think of some counter-plan. Goku arrives there as well and is healed by Dende. Goku suggests the merging technique Fusion, which he learned from the Metamorans. It is a technique where the power of the two who merge has to be equal, so they decide to teach it to Goten and Trunks.