Many years ago a great teacher oversaw a promising young pupil. It went bad, probably because he turned to evil or ended up showing his true colors, burned out or gave up. As the Master-Apprentice Chain continues, there's now a new student.
This student might have been Desperately Looking for a Purpose in Life and so the mentor really wants the student to succeed. It could be a means of atonement after whatever tragedy occurred. If the new and old student are Not So Different, it could be a means for the mentor to vicariously relive the first student's training and do it right this time. If the student went bad, teacher could plan to use his second chance and hopes that this new one can stay good.
It a subtrope to My Greatest Second Chance (for the mentor). This is what might come after A Pupil of Mine Until He Turned to Evil. It also related to Loving a Shadow, if the mentor focuses too much on the old hope through the new one..
- Fatal Fury: In the anime adaptation, Tung Fu Rue was sempai to Jeff Bogard and Geese Howard. However, Geese felt slighted when Tung chose Jeff as his successor and murdered him in retaliation. Years later, Tung takes Terry Bogard as his new pupil, and trains him in order to avenge Jeff's death.
- Jiraiya from Naruto sees teaching the title character as the only thing in his life he ever did right.
- The title character of Kenichi: The Mightiest Disciple is seen like this by his masters. They previously had Isshinsai Ogata as a disciple many years ago. The Elder recognized his sinister intentions right away, but Kensei and Akisame trained him for a while before his true nature became apparent.
- The Puella Magi Madoka Magica spinoff manga "The Different Story" reveals that Kyouko was Mami's apprentice, of sorts; until a horrifying incident made Kyouko turn extremely cynical and selfish, and they went their separate ways. Mami sees Madoka and Sayaka (mainly the former) as her second chance to raise heroic magical girls, like herself, and she gets quite emotional when Madoka promises to stay with her. Mami dies immediately afterward, and Sayaka crashes through the Despair Event Horizon, but Madoka becomes the savior deity of magical girls, so... third time's the charm?
- Ashita No Joe has the titular character become this for Danpei. He was a former boxer with a promising future until he lost his eye. Deciding to become a coach instead, he hit rock bottom when his pupil threw the match on purpose. It only takes seeing Joe win one fight for Danpei to kick his drinking habit and decide that he has found a new pupil.
- One can say that Assassination Classroom has Class 3-E for Korosensei. Because the last time he taught someone to become an assassin, his inability to empathize with his former pupil Reaper lead by the latter's betrayal, leading to the events of the series. Korosensei's tenure as the teacher for the Class 3-E really shows his Character Development, teaching assassination as a way to appreciate the value of life while exploring what they're capable of. In return, their confidence and faith in themselves have finally returned, enough to become successful in their chosen careers and paths, away from bloodshed and death. On the flipside, The Reaper knows nothing but a life of killing thanks to his teacher's assassination teachings emphasizing life as nothing but mere targets instead of valuable, and thus lead to his personality becoming twisted, and his eventual death. It's very easy to know what will happen if Korosensei wasn't present around Class 3-E (especially for Nagisa, who was very close to become a hitman due to his natural aptitude to kill, something that worries his friend Karma and the Class 3-E teachers), and what will happen if the original Reaper (aka Korosensei before the experiment) was kind to his pupil enough to prevent him to become a Deceptive Disciple.
- In Kung Fu Panda Tai Lung is the first devoted pupil of Master Shifu before the story starts. Now he is the enemy of Po and the Furious Five. His first "new hope" was Tigress but his reserved distance only led to a strained relationship. Shifu doesn't find inner peace until he successfully trains Po.
- Hercules is this to Phil in Hercules according to the latter, as he'd trained so many heroes before who "failed" to live up to their names.
- In My Little Pony: Equestria Girls, Sunset Shimmer herself implies that Twilight Sparkle was Celestia's new hope after Sunset decided to seek power for its own sake.
- Luke Skywalker from the Star Wars saga was started down the path of the Jedi by Obi-Wan Kenobi, who in the past taught Luke's father Anakin Skywalker before he turned to The Dark Side and became Darth Vader. Unfortunately for Obi-Wan, he didn't get to try to steer Luke away from the Dark Side before Vader killed him, and so the task fell to Yoda, the old master who had a part in training both Obi-Wan and Anakin.
- The Last Jedi also has this premise with Luke now as the broken old mentor and the new protagonist, Rey, as the pupil who "brings him back".
- In Harry Potter young Harry is wisely watched over by Dumbledore, who also kept a close watch over Tom Riddle before he became Lord Voldemort.
- This is part of the back story of The Giver: The Receiver of Knowledge who mentors Jonas is revealed to have had another protege in the past, hinted to have been his own biological daughter (in their society, children are assigned to parents other than their birthmothers), who committed suicide out of despair brought on by the knowledge she received from her mentor, and was unpersoned by the Community.
- This could very well be the case with Socrates and Plato, the latter being Socrates' best-known pupil. Socrates was known for having many students, some of which went bad. Perhaps the closest thing to a "Darth Vader" in ancient Greece was Alcibiades, a general who once served Athens but defected to Sparta... and a number of other places (long, confusing story there), but was generally seen as a pupil gone bad, while Plato went on to form an academy of his own to continue Socrates' work, the original Academy, in fact (in a grove sacred to the ancient hero Cadmus).