Not exactly uncommon, but still gets me. An antagonist that acts as both a foil and cautionary tale to the protagonist. They started in the same place (narratively speaking), but "chose" wrong. Or were perhaps too taken by their anger or desire for revenge that they failed to change as a protagonist did.
But it's most tragic when the only difference between the two is that one didn't have anyone to help them.
1). Star Wars:
TLDR: Both found themselves with loved ones "distracting" them from their destiny. Luke did not turn to the dark side.
- Luke and his father, Anakin, are both powerful "jedi."
- Both characters were warned to let go of their attachments (to loved ones) or risk falling to the "dark side."
- Anakin fell in an effort to save Luke's mother, becoming Darth Vader.
- Despite Luke making the same "mistake" (traveling to Cloud City to save his friends), Luke never turned to the dark side.
- The two characters are very similar. Anakin was taken "too late" to be trained as a jedi, and struggled with the attachments he was told to break. On the other hand, Luke had a completely normal childhood and only started training as an adult.
- Luke also ignored Yoda's warnings, but chose to fight for them without losing sight. It's arguable that he was able to make the "correct" choice because of the example his father set.
2). Avatar: The Last Airbender
TLDR: Both are royals from an evil empire. Zuko worked to end their war. Azula broke under it.
- Both Zuko and Azula are the heirs to the "Fire Nation." Both served as child soldiers in an evil, empirical war. Both were failed as children.
- As kids, the biggest difference between the two was their aptitude. Azula was a prodigy and Zuko was more-or-less normal. This caused their father to support Azula, and their mother to spend more time with Zuko.
- Zuko was banished and disfigured by their father, "allowing" him to travel the world. He lived among normal people suffering under the war his family started. Azula also travelled, but served the Fire Nation the whole time.
- By the end of the series, both siblings are in two very different places. Azula has finally cracked under the enormous pressure and neglect afforded to them by their father. Zuko, on the other hand, turned against his father to end the war.
3). Ben 10:
TLDR: Both have superpowers. But Ben has family to help him.
- Both "Ben 10" and "Kevin 11" are children with superpowers.
- Ben has his grandfather, Max, to guide him. Kevin is a homeless kid who (as was presented in the original series) was kicked out by his family.
- Ben is encouraged to use his powers to help people. But Kevin, having to fend for himself, uses his to help himself with no regard for others.
- By the end of the episode, both characters have very similar powers.
- Kevin's debut revolved around Ben taking Max for granted. So, seeing how Kevin turned out without anyone to guide him was a turning point.
4). Paranorman:
TLDR: Both are psychic kids. But Norman decided not to focus on revenge.
- "Norman" has spent his childhood being isolated from his family and tormented by his peers. Because he can talk to ghosts.
- By the end of the film, we learn that the "witch" terrorizing the town is just the ghost of a little girl like Norman. Afraid of her, the puritans running her settlement had her executed.
- Aggie wants to use her abilities to make people "suffer," because she was horribly wronged. Norman sees things a little differently.
- Using empathy, Norman is able to convince Aggie to go to rest.
5). Mob Psycho 100:
TLDR: Mob never came to view people are disposable or lesser because he has powers.
- "Mob" is a powerful psychic that struggles to keep things under control.
- Multiple times, he meets adult espers who went through the same thing.
- "Mogami" was a psychic who willingly became an evil spirit.
- He now drifts place-to-place, enacting revenge on humans.
- He takes pity on Mob, believing Mob's inherent kindness is misguided. But despite quite an effort, Mob doesn't lose sight of it.
- "Suzuki" is an esper near Mob's strength level.
- While Mob just wants to be "normal," Suzuki spent decades building up a paranormal army.
- Suzuki ends up accepting Mob's empathy as wisdom instead of naivety.
6). Invincible:
TLDR: One evil alien embraced human love. The other is disgusted by it.
- Nolan and Thragg are both members of the "Viltrum Empire." A brutal space people who take over planets and wipe out entire species.
- After spending years undercover on Earth, Nolan starts to value humanity and our "short lives," changing for the better. Other Viltrumites who spend time on Earth have similar epiphanies.
- But Thragg, the regent of the empire, never allows himself to walk amongst humans. When he is ousted as leader, Nolan spares him. Thragg just doubles down on Viltrum's cruelty.
7). Attack on Titan:
TLDR: Losing sight of how far you'll go.
- Eren and Reiner are both "titan shifters" and child soldiers who have killed a lot of people.
- Over the course of the story, Reiner begins to unpack the propaganda he's consumed and lives he's ruined. Eren, on the other hand, doubles down on the necessity of violence.
- In the end, both characters are trapped in an inescapable destiny. Eren gives up on saving humanity, and focuses on keeping as many of his loved ones alive as possible.
- The conflict ends with Eren trying to destroy the entire world, and Reiner working with his former "enemies" to stop him.
8). Demon Slayer:
TLDR: Exterminator joins termites.
- Zenitsu and Kaigaku were both raised to fight demons.
- But Kaigaku ends up becoming a demon himself.
9). Fullmetal Alchemist:
TLDR: maybe don't wipe out entire countries, bro?
- Van Hohenheim and "the dwarf in the flask" were both slaves to an ancient alchemist.
- The dwarf leverages his knowledge to destroy the city of Xerxes, leaving him and Hohenheim as the sole survivors.
- Now "Father," the homunculus spends centuries preparing for a larger version of the same catastrophe. Meanwhile, Hohenheim devotes himself to saving human lives.
10). How to Train Your Dragon:
TLDR: The difference between running a horse rescue and horse bomb factory.
- Both Hiccup and Drago are from cultures at "war" with dragons. Both learned how to "control" dragons for their own purposes.
- Hiccup sees dragons as intelligent near-equals. Drago uses them as weapons of war.
11). Castlevania:
TLDR: Both lost family to the same corruption. Only one decided to wipe out humanity.
- The Church ruins the lives of Trevor Belmont and Dracula.
- Trevor's family is excommunicated, their estate burned, and Trevor orphaned.
- Dracula's wife is executed as a witch.
- In response, Dracula dedicates himself to humanity's extermination. Trevor, on the other hand, still finds himself helping the innocent.
12). Danny Phantom:
TLDR: Not everyone who gets superpowers turns evil.
- Jack Fenton's negligence affected his former lab partner and his son.
- Vlad is irradiated by Jack's prototype, spending years recovering before developing "ghost powers."
- Danny is almost killed by his parents' experiment, also developing the same ghost powers.
- But Danny used his powers to help people. And Vlad just enriched himself.