The Main Idea
The Cseki Saga is a trilogy that's a spin-off on the Buu saga, just without Babbidi...or Buu...or Uub.
Part 1 introduces Ahatake's sister's for the first time and introduces Cseki. It also features Fusion much like the Buu saga, as Cseki was far more powerful than all the Character's even after training in the Room of Spirit and Time. It also shows Ahatake use of the SSJ2 and SSJ3 forms.
Part 2 features the Metamorese Art of Fusion, and introduces Lierra. It also feature the Dreaded Absorption technique, and Ahatake's use of Mimicry.
Part 3 is the 3rd and final part of the Trilogy, and arguably the shortest. It features the Elder Kai and Kibito-Shin, the Potarra Earring Fusion, Shenlong, and introduces Sake the Fused form of Ahatake and Android 0.