Someone is part of a group they hate. They've got a bone to pick with people just like them, to the point of wanting to kill them all. But if they hate that group so much, why don't they off themselves? Turns out that they DO, but don't want to die knowing the people they hate are still alive. So they keep themselves alive long enough to do, then finish with themselves.
Unsurprisingly this kind of character is Not Afraid to Die and may not even mind dying before by someone else's hand in an elaborate example of Suicide by Cop. They might literally be unable to terminate themselves until then. It might even be some form of atonement and/or revenge on their part; they take down a group they were once part of, then end themselves.
Might be why a Death Seeker who's completely mortal doesn't end their lives, beyond feeling Suicide Is Shameful or wanting to go down in a blaze of glory. The Hunter of Their Own Kind, genocidal Boomerang Bigot and Omnicidal Maniac likely has this "retirement plan" in place once they've wiped out their own group/race/everyone, though could they just as well believe they should stick around even if it's only because It's All About Me. Overlaps with Genocide from the Inside and No Place for Me There.
- In The Boys, all superpowers come as a result of exposure to a Super Serum called Compound V. While most members of the CIA sponsored group "The Boys" believe their groups exists to curb the worst offenses of the all too often immoral or amoral superpowered "heroes" the secret goal of their leader Billy Butcher is to eliminate everyone who has ever been exposed to Compound V, including in the end the Boys themselves and Butcher, since they've all taken it in order to be able to stand up the the supers in a fight.
- The Punisher Kills the Marvel Universe: In a What If? where Frank Castle's family was killed in a superhero battle instead of the result of organized crime, he decides to go on a murdering spree to eliminate every superhero and supervillain. Being one himself, he ends the comic by killing himself.
- Sin City: While he doesn't plan on it at first, Hartigan realizes that he has to die after killing Senator Roark's son (responsible for framing him and sending him to prison for eight years) to protect Nancy, since he's the only one who knows who she is (and his heart condition means he probably wouldn't have lasted much longer). He aims his gun so an old man dies, and a young girl lives.
- Terminator 2 Judgement Day: The reprogrammed T-800 sent to protect John Connor eventually agrees to work with him to stop SKYNET's creation and eliminate the T-1000 chasing after them. Once that's done, he makes his intentions clear to destroy himself so he can't be used to create SKYNET like the last Terminator was, though needs the Connor's help to do so because he cannot self-terminate.
- Balthazar from Baldur's Gate II: Throne of Bhaal is one of the Bhaalspawn, who sees their common ancestry (being descended from the late God of Murder) as inherently evil and plans to get the world rid of it. To this end, he, like most other Bhaalspawn, hunts and destroys his half-siblings in order to be the only one left to inherit their father's powersâbut unlike everyone else, he plans to kill himself as soon as he succeeds
- In Sonic Adventure, E102-Gamma, one of Eggman's most powerful robots, has a change of heart and decides to destroy the rest of the E-series robots in order to free the animals trapped inside them. After destroying the rest of them, he willingly allows himself to be destroyed.
- The Dark Everett from Cura Te Ipsum, believing himself too dangerous to be allowed to live, hops from universe to universe killing alternate versions of himself. He almost killed himself before finishing the job.
- Othar Tryggvassen, Gentleman Adventurer from Girl Genius hates sparks and wants to kill them all, including himself.