Insane Forgiveness

This is the tendency of some characters to forgive other characters no matter how serious the wrong. This includes those other characters Jumping Off the Slippery Slope, murdering loved ones, or raping the person granting the forgiveness. In extreme cases, a character granting Insane Forgiveness will grant it to someone who already crossed the Moral Event Horizon.

It's the principle of "forgive and forget" taken to extremes. Most viewers will be left scratching their head, wondering, "How can they just let that go?" Sometimes, other characters In-Universe also have this reaction.

This may be a trait of the Victorious Loser or The Messiah. Stupid Good characters do this as well; when they do, things tend to go wrong.

You may see this when Defeat Means Friendship.

Compare Easily Forgiven, which occurs when a specific character receives this from every good guy that matters.

Examples of Insane Forgiveness include:

Anime and Manga

Magical Girl Lyrical Nanoha has Fate who, shortly after her own atonement and Prescia's defeat, offers to save Prescia from dying because Prescia raised her like a daughter. After repeatedly abusing Fate, attacking the familiar Fate worked so hard to create, and nearly causing the deaths of countless numbers of people, most objective observers would say that Prescia wasn't worthy of Fate's consideration.
In Little House With an Orange Roof, protagonist Shoutarou tends to stress forgiveness way too often, such as when an adult man strikes his 5-year-old-step-daughter-to-be hard enough to knock her over.
Goku from Dragonball Z has a long list of people who've tried to kill him. Most of these people become his True Companions later and after that happens, he never brings up their previous transgressions.
Naruto toward Sasuke, after the latter has just about done everything but stab a puppy onscreen.
In the Yu-Gi-Oh! second anime (or at least the dub), Kaiba instantly forgives the Big Five for trying to kill him, or at least decides to hold off calling the police until after trying out this ~~obvious trap~~ new virtual reality device they've invented.
- Yu-Gi-Oh!: The Abridged Series naturally has a field day with this:

Mokuba: Big Brother, why are you acting so out of character?

Ranma ½: Ranma Saotome has forgiven and even really helped out many people who've tried to kill him, have kidnapped a loved one, or both. Does this guy never hold a grudge?
Code Geass: Ohgi still forgives Villetta, then a Britannian spy, for trying to kill him while she still hasn't given up trying to do so.
In one episode of Komi Can't Communicate, Yamai shifts from Clingy Jealous Girl to borderline Yandere by kidnapping Tadano, tying him up, and stowing him in her closet, outright stating she never intended to let him leave. The story took this all way too seriously for her to have meant it as a joke (and if she did, it was not funny), but oddly, she never faced any comeuppance for this at all. This is, by the way, a big reason why Yamai is despised by fans.

Fan Works

This is an common attribute of Albus Dumbledore in Harry Potter fan fiction, usually when he isn't actively malevolent: he is so devoted to "redeeming" Death Eaters that he will offer any number of "second chances" regardless of the atrocities they've committed.

Literature

In The Silmarillion, Manwe forgiving Melkor is a borderline example—even most of the other gods thought it was a bad idea. It was basically an Good Cannot Comprehend Evil situation. Notably, when Melkor rose up again, waged war in Middle-earth for centuries and then asked for forgiveness a second time, the gods just chucked him into the void outside of the universe.

Live-Action TV

Tori Vega of Victorious always seems to be able to let Jade West's behavior slide, no matter how awful that behavior might seem to the viewer. One episode even features a truly bizzare example of What the Hell, Hero? where the person being forgiven is the same person calling Tori out for it.
The Tenth Doctor from Doctor Who does this selectively. Unfortunately, the probability of his granting forgiveness is directly related to the horrors the person he's forgiving has committed, and often granted without there being a Heel Face Turn from the other party.
On True Blood, Sookie's Love Makes You Dumb is arguably bordering on this when it comes to Bill's various dodgy deeds.
On Buffy the Vampire Slayer, many fans felt this way about Buffy and Spike after the Attempted Rape. Admittedly, by the next time she saw him he had gained a soul and thus could be considered a different moral entity, but she showed signs of forgiving him even before that. Of course, their relationship was never really portrayed as healthy that season.
- It should also be noted that while she doesn't confront him about the rape attempt itself after, for many in-show months she noticeably flinches when he touches her and otherwise does her best to ignore his presence when she can. The forgiveness didn't come immediately, even when she found out he had a soul.
Chuck: It seemed like this trope applied to Agent Shaw and Sarah until The Reveal that he had been faking his forgiveness so he could get a chance to kill her: " You killed my wife. Did you really think I'd be okay with that?"

Oral Tradition, Folklore, Myths and Legends

According to the New Testament, Jesus, and by extension God, would be an example of this.
- That's provided the sinner is genuinely contrite, asks for forgiveness and accepts salvation. If they don't, there's a very different result...

Tabletop Games

In Dungeons and Dragons lore, Zauriel was the original ruler of Avernus, the first layer of Hell, until she was overthrown by her second in command, the pit fiend general Bel. For centuries, Zauriel was kept alive in the dungeons under the Bronze Citadel, subjected to horrible torture as jailers used diabolical devices to siphon her energy to fuel and empower Bel. Zauriel never accepted her fate, her rage and struggles in her attempt to escape causing Avernus itself to become more hostile, volcanic eruptions and meteor strikes blasting the surface. Eventually (as of 5th Edition) Zauriel did escape and seize back her role of ruler of Avernus. What did she do to punish Bel for betrayal and subjecting her to centuries of torture? Absolutely nothing, other than to demote him to his previous position as her second-in-command. Possibly she's being pragmatic, given how good a strategist Bel is, or possibly she puts most of the blame for it on Asmodeus, or possibly she even admires him for being so assertive (this is Hell, after all). Given the screwed up nature of diabolical politics, it could be all three.

Web Comics

According to Saturday Morning Breakfast Cereal, Jesus would be an example of this.

Western Animation

On Batman: The Animated Series, Harley Quinn pretty much always forgives the Joker no matter what, even when he tortures children and has tried to kill Harley in the past. In this case, she literally is insane, though, and the show makes it clear that this isn't a healthy relationship.