At some point, he became interested with supernatural hunting. In 2009, he began working with his husband, Jesse. They operated from Mexico to Texas. Upon realizing the Bisaans would return in 2016 to attack people in Jesse's hometown, they left their operating area to end the Bisaans problem forever.
When Dean tracked down an impregnated Libby in the forest, he was ambushed by a male Bisaan. Dean nearly lost the brawl, but thanks to Cesar's help, the Bisaan was decapitated. Jesse later came and stabbed the Bisaan multiple times just to make sure the creature was really dead.
They later shared their knowledge about Bisaan to the Winchester and how to deal with them. Cesar later teamed up with Dean to track down the Bisaan lair. In the lair, he encountered the females who had been killed because the Bisaan eggs development inside their womb. The two defeated the remaining Bisaan inside the lair. After Sam and Jesse came, they found the corpse of Matty and many of the Bisaan victims. After locating them, they give all of them the proper hunter funeral pyre rite and then destroyed the Bisaan lair.
In the aftermath, the Cuevas retired from the hunter works and returned to their home in New Mexico to breed horses.