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 who is not part of their kind.
- Biological Weapons Solve Everything: Using a biological weapon (weaponized disease) to wipe out the enemy.
- Death March: If large numbers of people from a targeted ethnic group are forcibly exiled from their lands in lethal conditions, then it can cross over to genocidal ethnic cleansing.
- Family Extermination: Attempting to eradicate an entire bloodline.
- The Famine: Although most famines result from natural or accidental causes, it can sometimes be intentionally planned (or at least maliciously neglected) by the government in efforts to allow entire communities to fatally starve.
- Final Solution: A plan to commit a complete genocide to permanently eliminate all "undesirable" people.
- Gendercide: Extermination of an entire gender/sex.
- Genocide Backfire: An attempted genocide ends with vengeful survivors now seeking retribution on those responsible for destroying their people.
- 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 decides to destroy their own people.
- Genocide Survivor: Someone who lived through a genocide.
- The Great Exterminator: Someone is famed for wiping out a pestilent species.
- Guilt-Free Extermination War: An all-out war that won't end until one side is totally exterminated.
- Inferred Holocaust: The work glosses over the fact that certain events have the most likely outcome of many people dying.
- Kill All Humans: Attempting to destroy all of humanity.
- Leave No Survivors: The aim of many planned genocides is the complete annihilation of an entire category of people (whether they succeed at doing so is another matter).
- A Nazi by Any Other Name: Someone demonstrates Nazi-like characteristics, such as extreme racial hatred and a desire to exterminate everyone they despise.
- Nice Job Breaking It, Herod: The villain fails to kill a certain child during a massacre, who is destined to ultimately defeat him.
- Omnicidal Maniac: The villain wants to kill everyone and destroy everything in the whole world (or known universe).
- Politically Incorrect Villain: You'd have to be both extremely evil and bigoted if you're willing to destroy an entire race of people.
- The Purge: An organization decides to eliminate every single member who dissents with them.
- Rape, Pillage, and Burn: An evil army decides to burn a whole city or town to the ground and massacre as many of its civilian inhabitants as they can.
- 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 wants to indiscriminately kill every single "monster", regardless of how good or evil they really are.
- Would Be Rude to Say "Genocide": The perpetrators of a genocide use dishonest or euphemistic terms, if not outright denying or excusing their atrocities.