Dragon Ball: Defiled Blood

Dragon Ball: Defiled Blood is a series that occurs many years after Goku died and Goku Jr's Grandson, Goken, is the protagonist.

Prologue
The world soon forgot about the legendary Goku and his descendants. Although a small threat rose occasionally, the next generation’s hero would put an end to these evil beings with ease. The modern evil wasn’t as strong as a Super Saiyan but Goku’s pure Saiyan blood was dissipated through his descendants. The further dissipated the blood was, the less Super Saiyan levels the descendant could achieve. The last capable Super Saiyan was Gotan. He could only demonstrate the Super Saiyan transformation, nothing more. But this time evil was patient. Gotan never got to slay a malevolent being. But evil waited for an opportunity to strike the Earth when no Super Saiyan existed. When only Gotan’s son, Goken, could defend the Earth. But he couldn’t become a Super Saiyan.