Ashe: Hunh!? What do you know about me!?
Master Albert: I know everything about you! As if you were my own daughter. I want you to grow! Evolve! Show me your strength!
So you have a pair of Arch-Enemies: a hero and a villain. And then... The villain gets interested in the hero.
The hero and villain are very similar to each other, and both grow aware of that fact. But they have different reactions. While the villain genuinely wants to take the hero under his or her wing, the hero is opposed to any friendly interaction—but may fear the villain has a point. The kind of obsessive behavior and mind games this generates on both ends is a prime source of Foe Yay.
If the hero and the enemy do end up becoming mentor and student, the ensuing relationship can range from the worst kind of Training from Hell to a downright parental role. Both will still probably end up at odds. And it'll end badly for at least one of them.
The Hero will usually consider The Mentor to be their Arch-Enemy and be very personally devoted to taking them down; The Mentor character is typically more amused by this than anything, and may take the role of a Stealth Evil Mentor. Foe Yay may lead to a Mind Game Ship, a Mentor Ship, or both.
- Gauron/Sousuke in Full Metal Panic!. The first time Gauron saw Sousuke, Sousuke was acting like a Creepy Child and throwing the dead bodies of all the soldiers he killed into a fire. And Gauron, being a messed up Ax-Crazy Psycho for Hire, took an instant liking to Sousuke. He asked Sousuke to come with him (with definite overtones of "there's candy in my van"), but Sousuke (wisely) refused. It's just too bad that Gauron isn't the type to take no for an answer and continues to mess with him any chance he gets.
- Kohei Kakihara and Chiko from The Daughter of Twenty Faces. Kakihara is fascinated by her fighting spirit. His obsession to take away everything Twenty ever had may have something to do with this as well.
- Orochimaru to Sasuke in Naruto, where the villain isn't just interested in the hero's potential but wants his body too. (No, not like that.) It's later revealed that Orochimaru tried to do the same thing to Sasuke's elder brother, Itachi. But he apparently stopped after he received an asskicking by him.
- Kyosuke to Kaoru in Zettai Karen Children. Incidentally, Kaoru also has a regular mentor, and the ultimate question of the plot is whether Kaoru will ultimately side with Minamoto or Kyosuke.
- Aizen's done this to a few characters. Orihime, for example. Once her powers came to Aizen's attention, he became very interested them. And when Masaki killed one of his hollow/shinigami experiments 20 years before the story began, Aizen became extremely interested in her. This interest extended to her son Ichigo and a good chunk of his Evil Plan revolved around nurturing and observing Ichigo's potential.
- In the final arc, Yhwach takes an interest in both Ichigo and Uryuu. Ichigo because of his complicated bloodline, and Uryuu because he was the only mixed-blood Quincy to survive the Holy Selection nine years ago. He succeeds at getting Uryuu on his side.
- For the dubious amount of villainy, Evangeline after defeating Negi says she won't kill him, because she found interest in him, but it's only when he ask her to teach him (after witnessing her power on a more serious level) that they become mentor and student.
- In Fate/Zero, Kirei Kotomine takes an interest in Kiritsugu Emiya, believing the two of them are Not So Different. He's wrong and is not happy when he realizes this.
- In Fate/stay night, Kotomine meets Kiritsugu's adopted son, Shirou and takes a similar interest in him. To his delight, he finds that unlike Kiritsugu, Shirou is just as empty as himself.
- Haman Khan finds herself intrigued by Judau in Mobile Suit Gundam ZZ, and alternates between fighting him and trying to make out with him.
- Berserk: When Guts first runs into Nosferatu Zodd, he puts up the best fight Zodd's ever seen from a human in three centuries. Which isn't saying much, as Guts and Griffith combined can't kill him. However, on seeing that Griffith has the red Behelith, Zodd spares the two of them, even going as far as to save Guts' life during a siege (Zodd was watching him fight an enemy general from several miles off when Guts lost his sword, Zodd immediately threw his own sword between them, allowing Guts to win). When Griffith starts the Eclipse, Zodd accepts the Skull Knight's request to interrupt their duel when he sees it'll save Guts. And later still, when Guts is prevented from taking a ship by Emperor Ganishka's attack, Zodd and Guts more or less willingly team up to send him back despite Zodd now being The Dragon to Griffith.
- Vampires in Seraph of the End usually find no interest in what humans are up to and hardly interfere in their affairs. Ferid is the exception as he is attracted to Mika and Yuu for their blood and their good looks.
- Stain from My Hero Academia actively likes Midoriya, who is one of the very few people he believes embodies what it means to be a hero. This is a major factor to why he saves a captured Midoriya from a flying Nomu.
- In the Ultimate Spider-Man line, the second Spider-Man, Miles Morales, is approached by his uncle, the super thief Prowler, for training. Little does he know, the Prowler needs Spider-Man to deal with the extremely powerful Maximus Gargan—the Scorpion.
- Ra's Al-Ghul to Batman. He sees Bats as Not So Different, and was once interested in him being the successor of his organization, The Demon.
- In the Green Lantern comics, Sinestro has taken an interest in Soranik Natu, the current Lantern from his home planet of Korugar. Where Sinestro was hated for being a Knight Templar tyrant (and the next Korugarian Lantern, Katma Tui, was hated by proxy), Korugar is coming to love Soranik. Both are viewing the peoples' growing devotion to her as practically asking her to be a dictator herself, which Sinestro views as her bringing order where he can't anymore while Soranik is greatly troubled by it. And it's no help at all that Sinestro is Soranik's biological father.
- Teenage Mutant Ninja Turtles: Like Ra's Al Ghul to Batman, the IDW version of the Shredder has decreed that only Leonardo is fit to inherit leadership of the Foot Clan.
- In Birds of Prey Lady Shiva takes an interest in training Black Canary.
- Shiva also took an interest in Cassandra Cain. Not because the teenager was her long-lost daughter but because she was one of the few on the planet who had a real chance of killing her in a fair fight.
- She also eventually feels this way about Huntress after the latter takes Canary's place during a battle to the death in order to save her friend, and gives Huntress the honorary name "Iron Owl" due to her refusal to go down without a fight despite being completely outclassed by Shiva in terms of skill.
- In fact, Lady Shiva is said to have a standing offer to anyone to train them, hero or villain. The price is that anyone who accepts, will have to face her in a Duel to the Death one year after they leave her tutelage.
- Judge Dredd: The main character of the "Fall of Deadworld" storyline, Judge Fairfax, was once an acolyte of Judge Death, who still wants to recruit him as one of his lieutenants after they had a falling out. Fairfax just wants to ride out the apocalypse.
- Orochimaru to the main trio of time travelers in the Naruto Fan Fic A Wrinkle in Time (Naruto). He states that he needs Sasuke for his eyes, so it doesn't matter whether or not he has talent. However, he wants those three for their talent, seeing it as being wasted on Konoha. It's incredibly ironic, seeing as the three time travelers in question are Naruto, Shikamaru, and Lee, who were all "dead lasts," for lack of a better term.
- In the sequel of Child of the Storm, one of Surtur's strongest minions - a literal dragon - claims this of his master in regards to Harry, claiming that Surtur wants to take him on as a no-strings-attached student in the belief that he would come to see that Surtur was right and that he should ally with him of his own free will. Harry, who's familiar with the well-earned reputation dragons have for manipulation and has heard speeches like this before (and wasn't interested then), laughs in his face.
- Rosario Vampire: Brightest Darkness: In Act III, it's revealed that this why Kiria didn't simply kill Tsukune and the others back in Act II; having seen the power of Tsukune's inner ghoul firsthand, he decided that it would be useful in his plans. Unfortunately for Kiria, he discovers the hard way in the final chapter of Act III that Evil Is Not a Toy.
- Soul Chess: Aizen took an immediate interest in Lelouch the day they first met, after Lelouch defeated him in a game of chess. At first he sought to make Lelouch an ally, but once it became clear that Lelouch would rather stand against him, he settled for making the former prince his main rival instead. Unfortunately, he greatly underestimated said rival and was subsequently killed and sent to hell for his troubles. By the end of the fic, Aizen came to hate Lelouch so much that his two main priorities were:
- And Then There's You: Since he learned he had a living, healthy grandson he could mold into his perfect heir, Ra's al Ghul decided to study the mother - Jason Todd. Due to Jason being the only known omega to successfully carry and birth a male alpha from the Al Ghul bloodline, Ra's strongly hints he would like to force Jason to produce more potential heirs.
- How on Earth?: Grandfather immediately takes an interest in Nigel Uno/Numbuh One after learning the latter is his only biological grandchild. With Nigel's father and uncle both inadequate successors for a variety of reasons, Grandfather plans on molding Nigel in their stead, and takes the first step by activating Nigel's latent superpowers.
- Star Wars:
- Luke Skywalker and Darth Vader have strong elements of this, minus the Foe Yay because, well, squick. The fixation leads to both Last-Second Chance and We Can Rule Together moments. Of course, from Vader's perspective, he is neither villainous nor beginning an interest.
- Also the Emperor toward Luke, believing (rightly) that he is stronger than his father.
- Palpatine has it to Anakin in the prequels too. He became something of a father figure to the young Anakin in the hopes that he might one day corrupt him to the Dark Side, though he didn't go full-on until he realized how much more powerful Anakin had become than his previous apprentice, Count Dooku.
- Kylo Ren in The Force Awakens offers to teach Rey in the ways of the Force (in the middle of a duel, no less!).
- Watanabe of Unbroken is fixated on Zamperini. He even tells him that from the moment they met, he knew they were alike and that they could have been friends if not for their opposing sides. Zamperini mainly just seems creeped out by the attention.
- In The War of the Ancients, it's implied that Broxigar's prowess during his final stand against the Burning Legion, during which he managed to lightly wound Sargeras himself is one of the reasons the Burning Legion tried to recruit the Orcs.
- In the Alex Rider series, the Big Bad of the third book Alexei Sarov takes an interest in Alex. He takes him hostage and tries to convince Alex to accept him as his new father due to Alex's similarity to Sarov's dead son.
- Hannibal basically runs on this, specifically Hannibal Lecter's interest in The Empath Will Graham.
- In the Supernatural episode "All Hell Breaks Loose, Part One" (S02, Ep21), the Yellow-Eyed Demon sees himself as Sam's mentor and Sam as his creation. Sam sees the Yellow-Eyed Demon as his Arch-Enemy.
Yellow-Eyed Demon: That's why I'm here, Sam. I wanna give you the inside track. You're tough. You're smart. You're well-trained, thanks to your daddy. Sam — Sammy — you're my favorite.Sam: You ruined my life. You killed everyone I love.Yellow-Eyed Demon: The cost of doing business, I'm afraid.
- Alaster, Abaddon, Crowley and The Darkness for Dean. So. Very. Much.
- Lucifer for Sam. Still.
- In Cutey Honey The Live, Panther Claw member Mayumi Karasugawa takes a keen, unhealthily obsessive interest in Sister Miki after initially believing her to be Cutey Honey. Even after she knows who is who, she still relentlessly pursues Miki.
- Terra and Kefka in Dissidia: Final Fantasy.
- In the Fan Sequel The Silver Lining, Graham has a strange vision where Manannan claims his real plan had been to treat Alexander as an apprentice and surrogate child. Alexander's reaction to the revelation is a combination of squick/horror/disbelief.
- In Star Wars: The Old Republic, the Sith Inquisitor is this for Padawan Ashara. They need Ashara's aid to get into the old Taris Jedi Temple. Now, being as you're Sith and she's a Jedi Padawan, there's already a problem. No matter how it goes, she ends up as your unofficial apprentice. The Sith Warrior does the same with Jaesa on Alderaan, as her ability to see through lies would be very useful to the Sith. Of course, it's entirely on you to live up to the evil Sith reputation or decide to be more Light Sided.
- In the Imperial Agent storyline, after the prologue missions on Hutta the Agent catches the attention of Darth Jadus, who wants them to swear personal loyalty to him. When you confront him at the end of Act I, he offers you the chance to serve as his personal agent and help him in his plans.
- In Fallout: New Vegas, if the Courier kills Vulpes Inculta of Caesar's Legion, Caesar himself will eventually offer the Courier full amnesty and a place at his side in the Legion, explicitly admitting he's impressed by how the Courier gets what they want.
- In The Elder Scrolls V: Skyrim, Hermaeus Mora, the Daedric Prince of Knowledge, is revealed to be very interested in those who are Dragonborn. In ages past, he seduced the First Dragonborn, Miraak, into becoming his champion in exchange for great power. In the main quest of the Dragonborn DLC, Mora orchestrates the situation as such to allow Miraak to think he could plot against Mora in Apocrypha, using the opportunity to secretly groom the Last Dragonborn as his replacement, and thusly allowed Miraak to become a threat the Last Dragonborn could not ignore. The Last Dragonborn foils Miraak's plans, Mora kills Miraak in a combination Impaled with Extreme Prejudice/You Have Outlived Your Usefulness killing, and the Last Dragonborn takes Miraak's place as Mora's champion, whether he/she likes it or not.
- In the Ensemble Stars! main story, Eichi genuinely thinks very highly of Trickstar's skill. In particular, he tries to recruit Hokuto and Subaru for his top-tier unit fine, as he believes there he could truly bring out their full potential. (It also has the added benefit of converting the current biggest enemies to fine, but he isn't lying about any of this, either.) Subaru rejects him immediately, as Eichi assumed his love of money means that he would be easily tempted by greed, but Subaru actually just likes shiny coins and has no interest in becoming wealthy. Hokuto is much more troubled, as his parents are both celebrities in the entertainment industry and joining a high level unit like fine seems like the logically 'correct' decision to follow their legacy. When he does (temporarily) join, Eichi seems to be genuinely trying to mentor him, teaching him that betrayal and sabotage are the only way to be successful in the entertainment industry. Naturally, Hokuto echoes this statement back when he switches back to Trickstar.
- In Drowtales, Snadhya'rune Vel'Sharen sets her sights on Ariel Val'Sarghress due to the latter's bloodline, which contains a potent Anti-Magic ability and Ariel's own unique sorcery. The first inklings of it appear all the way back in the third chapter, but it's not until chapter 47 that the two meet face to face and immediately attempts to earn Ariel's favor. It ultimately fails because Kalki attacks Ariel, and Snadhya is so incensed by this that she later murders Kalki in cold blood for disrupting her and outliving her usefulness. Previously this method had worked flawlessly when Snadhya recruited her other "proteges" or students who showed unique abilities, including Mel'arnach Val'Sarghress, Ariel's sister (actually her mother).
- Big Hero 6: The Series: Obake has taken a paticular interest in Hiro, to the point where some of his evil schemes amount entirely to testing Hiro and seeing how he reacts. To a lesser extent he seems interested in the other members of Big Hero 6 as well, but Hiro is the one with his focus.
- Robin and Slade from the Teen Titans cartoon. The similarity is emphasized whenever they fight each other, and especially when they fight together, as their fighting styles are nearly identical.
- To a somewhat lesser extent, this is observable between Cyborg and Brother Blood as well.
- Slade and Terra have a bit of this, too. Terra allows him to mentor her and...things go downhill. To make it worse, in the comic storyline this was based on, the two were actually in a sexual relationship, though Terra was slightly older (but still underage).
- Ultimate Spider-Man is a Spider-Man franchise that justifies Peter's and Harry's friendship through this. Harry was nice one day and decided to give Peter a ride home instead of letting him walk through the rain. Harry's father, Norman, had heard of Peter's good grades and encouraged the friendship in the hopes that Peter would be a good influence.
- Danny and Vlad from Danny Phantom. Vlad is fixated on Danny's mother, Maddie, and ultimately hopes to steal her away from Jack. Add the fact that Vlad and Danny are pretty much the only half-ghosts in existence, and Vlad sees Danny as the perfect Child Substitute. Naturally Danny doesn't see it this way.
- Rex and Van Kleiss from Generator Rex. Although it seems that he is more interested in Rex's nanites than the boy himself.
- Van Kleiss himself supplied that he would be happy if Rex was a vegetable as long as he was still breathing. Unlike some other examples, Rex takes advantage of this without entering such a relationship. In the episode "Alliance" Rex uses guile and half-truths to undermine Van Kleiss in various ways. Most notable of them is getting Circe to defect from the Pack. Circe was convinced that Van Kleiss wants to take Rex in like he did with her. So when Rex is forced into an arena with No-face for a no holds barred beatdown, Rex makes it clear to the onlooking Circe that Van Kleiss places no value on him other than his life.
- Omi and Chase Young from Xiaolin Showdown.
- Big Bad Nerissa in W.I.T.C.H. has an obvious interest in Caleb since he's her son. She tries to persuade him to her side and he flat out denies her.
- Star Wars Rebels: Darth Maul quickly takes a shine to Ezra and seeks to make him his apprentice. Everyone and Ezra says no but Maul is so unhinged/determined that he honestly seems oblivious to any protests. Maul is making more progress with his protagonist than other examples but his own ruthlessness is spoiling his attempts.
- This interest is later hinted to hinge on Maul projecting onto Ezra his longing for his former apprentice and brother, Savage.
- Storm Hawks: Master Cyclonis is very interested in Piper due to her natural talent in harnessing the power of crystals, an ability they share in common. The interest was originally sparked when Cyclonis attempted to infiltrate the Storm Hawks and befriended Piper to achieve that goal. Of course, there are hints afterwards that Cyclonis's interest in Piper goes...beyond her potential as an asset.