One side attempts to kill (almost) everyone on the opposite one based on their background. Most of these can be described as genocide, or sometimes even omnicide in more speculative works.
Motivations vary, but they most commonly tend to be employed by either xenophobic racists, fantastic or otherwise, or by the heroes against groups of beings who are (perceived to be) all pure evil. The former will often signify a crossing of the Moral Event Horizon, the latter makes the protagonists morally grey Pragmatic Heroes depending on how the work handles the implications of such an extreme action.
- Absolute Xenophobe: A group kills everyone not part of their kind.
- Biological Weapons Solve Everything: Using a biological weapon to wipe out the enemy.
- Evilutionary Biologist: The villain wants to better the human race on their terms, which may involve killing everyone they deem genetically inferior.
- Final Solution: Using genocide to get rid of the enemy.
- Feeling Oppressed by Their Existence: A character feels prejudiced towards a group even though the group has never harmed them in any way.
- Gendercide: Killing an entire gender.
- Genocide Backfire: An attempted genocide ends with a survivor now wanting to make those responsible for their kind being wiped out pay.
- Genocide Dilemma: The hero can't decide whether the best way to deal with the Always Chaotic Evil race is to wipe them out completely.
- Genocide from the Inside: Someone wipes out their own kind.
- Guilt-Free Extermination War: An all-out war that won't end until one side is exterminated.
- Inferred Holocaust: The work glosses over the fact that certain events have the most likely outcome of many people dying.
- Kill All Humans: A being wants to kill all humanity.
- Leave No Survivors: A killer murders everyone who comes in their path.
- Master Race: People who feel that their race is superior to all others.
- Misanthrope Supreme: A person who despises all of humanity.
- A Nazi by Any Other Name: Someone demonstrates Nazi-like characteristics, such as a penchant for exterminating races they despise.
- Nice Job Breaking It, Herod!: The villain fails to kill a child who is destined to defeat him.
- Omnicidal Maniac: The villain wants to murder everyone.
- Politically Incorrect Villain: You'd have to be evil and bigoted if you're willing to kill an entire race.
- The Purge: An organization slaughters everyone who dissents with them.
- The Social Darwinist: The villain believes only the strongest should survive and that everyone weaker is better off dead.
- Van Helsing Hate Crimes: A monster hunter who targets monsters who aren't intentionally hurting anyone.
- Would Be Rude to Say "Genocide": The people causing the genocide try to use more benign-sounding terms for the deed to sugarcoat the fact that they're killing an entire race.