WARNING: Spoilers follow for Amazing Spider-Man #51.LR by Nick Spencer, Matthew Rosenberg, Federico Vicentini, Marcio Menyz and VC's Ariana Maher, on sale now.
When the mysterious Kindred betrayed Sin-Eater, humiliated him and left him for the police in Amazing Spider-Man #50, it seemed readers had seen the end of the reborn serial killer who'd been targeting Spider-Man's other foes.
However, Sin-Eater is still around, has plenty of followers and even has a plan to try to win back over his master's trust in Amazing Spider-Man #51.LR. While Kindred has nothing left for Sin-Eater to do, it seems the villain finally lost his grip on reality and plans to cleanse the sins of another villain: the vampiric Morlun.
After Sin-Eater cleansed Norman Osborn and took on the final powers he needed to for Kindred, he waited for his master to come and reward him. However, when Kindred showed back up, he taunted Sin-Eater and made fun of him. He said he could barely stand to look at Sin-Eater and called him a hypocrite, a man guilty of sin trying to stand in judgment of others. While Sin-Eater claimed his sins were cleansed in the fires of hell, Kindred said there was one sin that the man never admitted to and was never cleansed of: the killing of his own partner on the police force, who murdered him in cold blood. With this, the Kindred then cleansed Sin-Eater of all the sins.
When Kindred woke up, he was surrounded by a few of his followers who had rescued him. Many of his followers were arrested in the attack on Ravencroft, but there were still some who found him and were able to bring him back to his base. There, he had one more dream of killing his own partner. After he awoke, his men showed him videos of the spider-powered heroes destroying Manhattan, possessed by Kindred and the powers Sin-Eater previously stole.
Sin-Eater spent a lot of time alone, contemplating his actions and believing that he needed to redeem himself in the eyes of Kindred. Being cast aside by the demon seems to have broken his mind. He believes it is now his duty to hunt down the spider-powered heroes and defeat them in his master's name, even though they are all following his master's commands. Sin-Eater said he will not stop serving Kindred and will defeat these heroes, believing that is what his master wants. He plans to cleanse Morlun and steal his powers to achieve this goal.
Although Morlun was originally created by J. Michael Straczynski and John Romita, Jr. in 2001's Amazing Spider-Man #30, he most recently appeared in the pages of Spider-Geddon. In that crossover, the heroes from the Spider-Verse had to team up again, with everyone from Miles to Spider-Gwen, Spider-Ham, Spider-Man Noir and more. The vampiric Inheritors made their return thanks to a mistake by Superior Octopus, and Morlun and his family were back to start feeding on spider-powered heroes once again. The battle ended with Morlun's father and siblings defeated, and all his siblings reverted into babies to give them a fresh start. However, the last scene of Morlun in that story showed Spider-Man wanting him brought in and turned into a baby as well.
Clearly, Morlun is still out there, and now Sin-Eater is hunting him down to take the battle to Spider-Man's allies.