In anime, it's not unheard of for the heroes to save their villainous counterparts. Intending to embody the best in humanity, they have oftentimes saved their antagonists even at great risk to themselves - whether or not the audience agrees with the decision.
However, the converse can also be true, albeit often for less magnanimous reasons. There have been a handful of instances where villains have saved the hero from what would have certainly been a disaster. Through identifying these unlikely acts of charity, we can fully appreciate their motives, whether intended or not.
10 Pain Resurrected Most Of Konoha (Naruto)
When Nagato was confronted by Naruto Uzumaki, he was reticent to hear reason and attacked him with what anemic strength he had left. Nonetheless, the intrepid hero persisted, stating what their master would have wanted and what was best for the world.
Finally, the Akatsuki leader agreed to revive everyone in Konoha - even including Kakashi Hatake. However, his body was already exhausted, and the jutsu put an enormous strain on it. Ultimately, his decision to revert the damage he caused would cost him his own life - a stipulation Konan was sure to warn him of.
9 Esdeath Saved Tatsumi From A Giant Monster (Akame Ga Kill!)
After both Tatsumi and Esdeath had been banished to a remote island by Syura, they quickly discovered that they were not alone. Giant monsters inhabited it, ones sharing Dr. Stylish's likeness with bloodthirst to match.
Esdeath proved to be a vigilant partner, leaping into action on Tatsumi's behalf and using her ice magic to obliterate their towering opponent. It was an excellent display of her love for the young Night Raid member - and proof that she is not to be crossed.
8 Hisoka Saved Gon From Failing The Exam (Hunter X Hunter)
During the Hunter Exam, Gon was instructed to take Hisoka's badge in order to proceed to the next tier of challenges. This was incredibly difficult to accomplish considering that his target was a Nen user, distinguishing him from many of the trial's other contenders.
Though Freecss was able to seize his badge initially, Hisoka was more than equipped with the strength to take it back from him. However, he wanted to see Gon advance in the Hunter Exam and succeed in life - only by doing so would he become "ready" for a brutal fight to the death later in the future.
7 Yuya Fungami Saved Josuke From Terunosuke (JoJo's Bizarre Adventure)
Terunosuke was a horrifying Stand user who was able to condense anything into paper - including humans. After kidnapping Koichi and Josuke's mother, he managed to make the hero slip up, displaying signs of fear and succumbing to his special ability.
Though there was no one else around at the time to save Higashikata, his salvation would come in the unlikely form of Yuya Fungami, a former enemy who he healed to aid him. While Highway Star was unable to defeat Enigma, Yuya did manage to free Josuke, allowing him to triumph over their foe on his own.
6 Bertholdt's Colossal Saved Armin's Life (Attack On Titan)
Bertholdt was the Colossal Titan and perhaps the most significant threat at the battle of Shiganshina. Unfortunately, he was also the only villain to have been captured despite the victories over Reiner and Zeke.
The Eldians understood that by taking prisoners, they were able to resuscitate those badly wounded in the fighting and gain a titan of their own. Through Bertholdt's (non-consensual) sacrifice, they were able to return Armin to health and acquired a massive advantage over Marley.
5 Bradley Killed Isaac McDougal (Fullmetal Alchemist)
Isaac McDougal was a terrorist that used his ice alchemy in order to pose a threat to the people of Amestris. His main demand was to expose Bradley, correctly calling out the corruption in the heart of the capital itself.
Though the Elric brothers (along with Armstrong) were able to force him on the run, it seemed as if he would abscond into the night. However, the homunculus himself was waiting for his opponent in a dark alley, more interested in keeping his intentions a secret than saving the people he swore to protect.
4 Satsuki Kiryuin Joined Forces With Ryuko (Kill La Kill)
Since the beginning of the series, Satsuki Kiryuin has presented herself as a threat to Ryuko. She claimed to have murdered her father and regarded those beneath her station as expendable fodder. This (understandably) bred animosity between her and Matoi, especially with how she turned Mako against her.
However, it was all an elaborate ruse in order to placate Ragyo and devise a plan against the life fibers. When the time came, Satsuki was willing to do anything to reunite with her sibling and defeat their mother - even if it cost her her own life.
3 Wamuu Gave Caesar A Life Saving Antidote (JoJo's Bizarre Adventure)
During their first battle against one another, Joseph Joestar insisted to be given more time to train so that he would pose an adequate challenge to the Pillar Men (as he was currently easy prey). Wamuu agreed to this under the stipulation that a ring be placed in his chest. It would dissolve gradually over one month, killing him when it completely evaporated.
After Caesar had stormed the Pillar Men's base and confronted Wamuu, he was defeated for his carelessness. However, the villain was touched by his performance and gave him the antidote to his friend's malady as a consolation.
2 Sasuke Spared Naruto At The Valley Of The End (Naruto)
After leaving the village, Sasuke faced a reckoning with his Team Seven companion, Naruto. This resulted in a climactic fight at the Valley of the End, one which saw both boys pushed to their limit.
Ultimately, the Uchiha was victorious and knew that killing Naruto would have progressed his Sharingan. Despite its benefits, he declined the chance to take his life, citing he would not need it in order for his power to grow exponentially.
1 Reiner Saved Everyone From A Titan (Attack On Titan)
During the night of Zeke's attack, a titan had broken into the tower the scouts were occupying. At such close range, their ODM gear would be inefficient, and their cannon only temporarily halted the intruder.
Reiner saved the group by hoisting the monster on his back and throwing it off the tower. Considering that the titan could have murdered everyone inside (except Ymir) with its proximity, he was under no obligation to do so in order to maintain his identity.