Are you referring to the rumored Alternatealternate ending of Death noteNote?
From deathnotefanon.wikia.com :
The Death Note alternative ending is a possible ending to show something else that might have happened to Light Yagami after his death. It is unknown if the ending is real or fake. There is a lack of evidence to prove the ending to be real. It has really only been seen on the Internet and there are mainly English versions of the ending circulating, but it has become popular in the Death Note fandom.
Due to the fact that there is no proof, it’s left to fans to decide for themselves. The ending only exists in manga form; there is no anime adaptation for the ending.
But in this ending Light decidedecides to die in old age and tell Ryuk to kill him. After his death he appearappears in the Shinigami Realm and startedstarts dying gainagain and again in the wayways his victimvictims died. Then light tellLight tells Ryuk to take him to theretheir king, so that he can make deal with him. He even toldtells that he will kill theretheir kind if he didn't agreeddoesn't agree. But in the end they just showedshows the start of theretheir journey, there's no interaction withwith the king.