Most anime adaptations of Osamu Tezuka's manga get this, as most of the great man's work, while having a generally cartoony look & feel with an uplifting message, still involved copious amounts of death and destruction (Lost World, one of his earliest forays into the world of boys' adventure stories was infamous at the time for having the highest body count of any manga up to that point, with only three members of the cast surviving to the end of the book). In more recent years this has started to swing the other way, though (the Metropolis animé is far more bloody than the original, and the 2003 Astro Boy series' version of Dr. Tenma takes the Evilutionary Biologist gimmick that was only briefly touched upon in the manga and turns it up to 11).
The anime series is filled to the brim with violence, screams, dismemberment and High-Pressure Blood, but when you consider that the original manga is more brutal in practically every conceivable way it doesn't look so horrifying in comparison. In particular the anime toned down the scenes of torture and sexual violence, such as by removing being raped as a child from Guts' backstory and leaving Wyald and the Black Dog Knights out of the plot. Despite this, it still shows the Eclipse in all its horror.
Kentaro Miura, on one of his breaks from Berserk, created a six-chapter long manga called Gigantomakhia which is considerably more lighthearted and idealistic than his main work.
The Black Jack TV anime series adapted stories from the manga, but occasionally removed some of the downer material.
In the manga story "Thieving Dog", a dog dies saving Jack and Pinoko from an earthquake, while in the anime the dog survives the incident and becomes their pet.
In the manga story "Sometimes Like Pearls", Jack's killer whale friend dies of injuries acquired while attacking fishing boats and killing fishermen. In the anime adaptation, "The Gift From a Killer Whale", the whale was hurt fighting another whale who was attacking the fishing boats, and is proven innocent just in time for Jack to save him.
Cross Ange is a very dark and depressing series about women who cannot use Mana being forced to fight against huge dragons coming from a different world just to pay for their upkeep. Cross Ange Academy meanwhile turns the episodes aired into one of the most light-hearted and funniest canonical spin-offs ever made. In fact, it's recommended to watch one episode of the anime then read the manga corresponding to the episode number.
Arguably every incarnation of Cutey Honey other than the original manga, even the darker toned Shin Cutey Honey doesn't escape from this. While most subsequent adaptations focus on Fanservice and violence, the original manga is full of Black Comedy that borderes on proto-Dead Baby Comedy, many characters died and it was played for laughs, many ugly girls tried to rape Honey's friend Natsuko and even the dirty jokes are far more kinky and hardcore: for example, towards the end of the manga Junpei, a 10-year-old boy licks Honey's crotch while she is naked and only covered in gold paint, and also everyone dies but Honey, the Hajami family and Panther Zora. Taken a step further with the 90's version, Cutey Honey Flash, as this version is a magical girl series in the same line of Sailor Moon.
The 1972 anime adaptation of Devilman was considerably lighter and softer in comparison with the original manga: Lots of changes to the story were made, the violence and nudity were considerably toned down, comic relief was included, and the most of the character whodied at the end of the manga are still alive in the last chapter of the first anime series, which also has a Bitter Sweet Ending instead of the tragic conclusion of the manga.
Not quite to the same degree, but the manga adaptation of Fate/stay night itself is leaning in this direction. It was already focusing mostly on the 'Fate' route of the visual novel, which is notable for being the most idealistic of the three routes, but then went even further by removing the multiple rapes and other trauma in Sakura's backstory, and humanizing and sparing the life of Shinji.
The original Fruits Basket is noticeably darker than the anime. Even without trimming some drama here and there, the anime covered the Lightest and Softest part of the manga, cutting off before the main plot really even started. Besides that, the two darkest characters were also the ones that deviated the most from their characterization in the manga: Akito was simplified into a fairly standard villain, and Shigure was relegated to comic relief.
The primary mech is a ridiculously cute mascot character named Bonta-kun, which can only "speak" by squeaking a high-pitched "Fumoffu!" Sandwiched between the original, serious series and the Darker and Edgier The Second Raid, it makes the differences all the more pronounced.
The fluffy Bonta-kun suit is also quite literally both lighter and softer than the huge metal mechas from the original and "The Second Raid."
The Getter Robo 70's anime series removes the batshit insane elements the original manga had. Ryouma becomes a virtuous, Hot-Blooded straightforward hero, while Hayato becomes the archetypical 'cool guy' loner... all in high school setting. They're still Hot-Blooded, though. But just try to compare that version to the latter closer-to-manga versions (Shin vs Neo, Armageddon, NEW)... where they're both Ax-CrazySociopathic Heroes with the side order of Hot-Blooded.
Ginga Kikoutai Majestic Prince is rather light and soft after Hirai's previous works. It has some of the most adorable funny expressions to grace a Hirai anime.
SD Gundam Force. It's Gundam, but all the characters are chibis, everything is completely light-hearted, and hardly anyone ever dies. Though it can have its Nightmare Fuel-like moments. That said, it's only slightly lighter and softer than some of the SDGundam stuff that preceded it...
Turn A Gundam is decidedly less (visibly) brutal than many of Tomino's other Gundam works, with more lighthearted and very optimistic (or at least hopeful) themes. Not surprisingly, Tomino worked on the series after recovering from depression.
The three OVAs of Gunsmith Cats, in addition to telling their own storyline rather than risking trying to adopt the manga storyline, also toned a lot of things down. May Hopkins' status as an underaged child prostitute and her sexual fetish for explosions and the scent of gunpowder, Rally Vincent's tendency to stop her opponents by blowing off their fingers or arms, the firepower of May's hand grenades, the general copious amounts of death—all of it went out the window. It is still pretty violent, though.
Higurashi: When They Cry: Rei and Kira. Before they came along, Higurashi itself was about murder and mystery, and had various recurring characters beating other people to gory pulps. Rei becomes much lighter in tone after Takano's defeat at the hands of the club and their friends in Matsuribayashi-hen, especially with the hilarious pool episode. And then Kira comes along, and it's much lighter than Rei in every way, with things ranging from Rika and Satoko becoming Magical Girls to hilarious and absurd situations happening during dates between Keiichi and the Sonozaki twins along with the other female protagonists, and even Keiichi ending up dating Oryou, Mion and Shion's grandmother. To say nothing of the KeiichixSatoshi yaoi joke from Kira. No, really. Just compare the openings of season 1 and Kira (season 4). Warning: watching them in succession can result in Mood Whiplash.
Despite opening with a quite massive Downer Beginning that isn't in the manga, the Kotoura-san anime is this overall, significantly toning down certain parts of the original yonkoma.
Episode 3 has Manabe beaten up significantly in the anime. In the yonkoma, he got stabbed, and was not conscious when Kotoura came to check on him. Also, Hiyori convinces the thugs to go after Manabe by telling him that he's stalking her. In the yonkoma, she tells them he raped her.
In the anime, one story arc has a criminal prowling the streets savagely beating up schoolgirls, resulting in them getting hospitalized. In the yonkoma, the criminal actually rapes and murders them.
Japanese fans of Lupin III were quite nonplussed when The Castle of Cagliostro hit theaters, as Miyazaki had made the normally-obnoxious Lupin and his cohorts unrecognizably nice. The film originally flopped at the box office. It took the passage of years, and fans who were able to see the movie on its own merits, for it to gain the popularity and critical acclaim it has today.
The same could be said of the second Lupin anime series, which is a lot goofier in tone than the original comics and 1971 anime series. Not to the degree of Cagliostro, but it definitely fits this trope.
The anime version of Magic Knight Rayearth does this with Alcyone's death. Not only does Alcyone not die after the first failed attempt at killing the Magic Knights, but she actually gets to redeem herself and save Cephiro in the second season.
Subverted when Presea is actually killed off. In the manga she never dies though so naturally the anime fixes that.
In the Mai Hi ME manga, the only person who dies at any point is an Asshole Victim who previously tried to sexually assault Shiho. After the characters work through their competing approaches to fighting Orphans in the first arc, they work together against common enemies, instead of being manipulated into fighting each other like in the anime. The characters also suffer significantly less emotional trauma than they do in the anime. A notable example is that Akane is able to win her fight and profess her love to Kazuya without her CHILD (and Kazuya by proxy) being killed and her descending into an Angst Coma.
The Mai-Otome manga is similar, with Nina remaining emotionally stable and loyal to the heroes the entire time, largely related to Erstinsurviving, and Arika and Mashiro never quite sink to the depths of despair that they do in the darker parts of the anime. On the other hand, several characters who survive the anime are killed off, and Sergay is arguably more evil than the Otome anime version of Nagi.
The Mai-Otome anime can also be considered this in comparison to the Mai Hi ME anime, as while the story is, in the best of times, more serious, it never seems quite as dark or hopeless, and there are fewer character deaths, although they are more often permanent.
The Melancholy of Haruhi-chan Suzumiya, a web series spin off of a similarly titled blockbuster franchise, seems very much a lighter and softer take on its source material, rendering every character as a Super-Deformed version, recasting Yuki Nagato as an eroge-obsessed otaku, and generally coming across as the original series' writers, animators and voice actors just having fun with the source material.
Though the intro in episode 1 promises that the series will eventually get hit with Cerebus Syndrome, Boruto starts off this way compared to Naruto. It's justified in that the characters are living in an era of peace. They start off as academy students rather than genin, so they don't have any worries, and the episodes have light-hearted stories with no dangerous fights. Even after becoming ninja the main cast lack the Dark And Troubled Pasts of their predecessors. According to Boruto: Naruto the Movie even their chunin exam is a walk in the park compared to their parents (having no apparent deaths or serious injuries and featuring a game of catch the flag rathed than dropping twelve year olds into a dangerous forest). Word of God is that Boruto is aimed at a slightly younger audience than Naruto Shippuden.
Girlfriend of Steel does this too, obviously. Everyone seems to be alive and flourishing. Rei is a Genki Girl. Yikes. Oddly enough despite that Rei has the exact same backstory.
Dual! Parallel Trouble Adventure takes the general characters — a brown-haired boy with parental issues, a complex soul tie to a giant mecha, and rare hallucinations, a tsundere girl trying to prove herself, and a partially alien 'soul' inhabiting an artificial body with the resulting identity and self-worth issues — and setting of Neon Genesis Evangelion and looks at how it'd perform if everyone involved was at least sane enough to have not taken a pencil to their eyeballs long ago. Given that it belongs to the Tenchi Muyo!Multiverse it's hardly surprising.
Argento Soma, another Take That! series, is still fairly grim, and its heroes are still full of issues, but overall seem to cope pretty well, up to making the half of the cast Warrior Therapists, as the authors believed that being badass makes wonders with one's mental health.
Probably the best example of this trope in regards to EVA spinoffs is Evangelion @ School (or Petit Eva), where there are chibis of MASS-PRODUCED EVAS!
The Ayanami Raising Project games, where the player takes the role of a 2nd lieutenant at NERV and helps raise Rei (or Asuka, depending on the campaign). Despite running concurrently with the anime series and occasionally going through its events, the games are light, fluffy and absolutely adorable.
Pokémon is considerably lighter and softer than the games, as while the games are generally light, they do delve into dark elements, especially in the villains and Pokédex entries. The anime doesn't have that. Some dark elements still show up on occasion though, especially in the movies. In the show itself, they just don't stick very long.
Example A: Due to trauma stasis, the two episodes involving Team Plasma fighting Team Rocket and creating mass destruction in Castelia City were not aired, and the Team was introduced in a different way in their less morally ambiguous Black 2 & White 2 forms.
The anime itself has gotten lighter and softer over time. It's most noticeable with the violence. Violence against humans, comedic or otherwise, isn't as common or as graphic as it was in the first seasons. Battling is also less violent.
The games make it clear that Pokemon eat each other and many Pokedex entries are quite dark. The anime, early episodes aside, avoids implications of eating Pokemon and often changes Pokedex entries.
As both series are intended to be comedies to the core, it would be inaccurate to claim that either version of Ranma ˝ is Darker and Edgier then the other. The anime version can still be seen as lighter and softer then the manga. Not only does it lack the somewhat darker storylines that the author created after the anime was cancelled... which includes, among other things, a Villain of the Week whose father was technically killed by Genma, Ranma meeting his mother — and then being threatened with Seppuku because Happosai dressed him in girl's clothes, Ranma being trapped in female form by a group of more powerful and much more vicious martial artists, and Akane being kidnapped, near-drowned and then changed into a doll, an almost fatal experience, over Jusenkyo... but also removes several of the more Comedic Sociopathy moments from shared storylines. Examples of this include Akane's viciously vindictive speech to Ranma after the first Nekoken incident, Happosai's attempt to murder what he believes is baby PantyhoseTaro because he thinks Taro will become an even better Panty Thief then himself, and the ending of the Hypnotic Mushrooms story, which in the anime ends with a gag and in the manga ends with Akane surrounding herself with weapons to use against Ranma if he "tries something" while Ranma gives her a Deadpan Snarker response.
The anime adaptation of Rosario + Vampire definitely is this. It cuts out most of the darker story arcs that crop up later in the storyline, while considerably softening many of the earlier ones, and generally portraying a lot of antagonists as less evil than their manga counterparts. For example, the Attempted Rape element of Mizore's introductory arc was removed completely, while Ruby's master Yukata, a notable Knight of Cerebus, was reduced to a tragic Posthumous Character. Finally, Tsukune's ghoul transformation, a major contributing factor to the series' Cerebus Syndrome, was ignored completely.
Sailor Moon played this straight for Pretty Guardian Sailor Moon. Some elements were toned down in the anime compared to the manga, but it wasn't lighter. For instance, in the first story arc, only Usagi dies (from using the crystal's full power) and Mamoru revives her with a kiss; whereas the anime version had everyone brutally die in pure Nightmare Fuel. Also done in the anime itself with the SuperS season, after the previously unseen level of darkness in the preceding S season.
While School-Live! is still a pretty dark and depressing series, the anime softens up the tone considerably by having even more lighthearted and comedic moments then what the manga already had, as well as having more emphasis on the Slice of Life element of the series. Plus the anime ends on a bittersweet but optimistic note. The anime leaves out some of the really dark events, such as extra casualities for some Red Shirts that Miki and Kei met at the shopping mall, Yuuri having a massive mental breakdown that wrecks her sanity completely, and the implications that the cure used on Kurumi needs to be taken weekly or she'll become a zombie again. The anime ended before the University arc, which was the point when the manga got really dark.
There is a chance that the Shiki anime is this compared to the manga and, especially, the original light novel. At least one character had his worst traits from the manga sanitized in the anime to make him more sympathetic, and in the original light novel Natsuno never rises from the dead, while in the manga and anime he does. Of course, even if this is true, the anime itself is still really, really dark!
The anime adaptation of the original Slayers novels has its fair share of emotional turmoil and grisly moments (enough to be denied the right to air on the old Fox Kids network back in the late 90's, believe it or not), but in general it is much lighter in tone and sillier (replacing the female protagonist's First-Person Smartass humor from the novels to slapstick). Also, the character Xellos, an Affably Evil demon-priest, is far more sadistic in the novels, whereas his affably-evil attitude in the anime makes him comical. A story involving a cult supporting the world's Big Bad was also never bought into anime form. Most of the manga and video games that followed are also this trope.
Soul Eater's sidestory manga from the same mangaka Soul Eater Not! appears to be a twist of this from the first three chapters. It is focused on a period prior to Sid becoming a zombie (an event from Chapter 1 of the manga) and looks at how new normal academy students (instead of how badass seniors) fit in. Along with how students can raise money, waste money, get their names (Eternal Feather for example) and live in academy quarters.
Stitch!, the anime adaptation of Lilo & Stitch and Lilo & Stitch: The Series, is not just more lighthearted than the originals, but also replaced the human characters, and is possibly an alternate version of the series entirely.
In the original H-Game series, there was only one penalty for losing which applied to all matches: the victor had to leave the ring, while their opponent was publicly raped by members of the audience, or the tournament committee.
The original Yu-Gi-Oh! manga was quite violent and bloody, especially in early chapters when Duel Monsters wasn't as big of a thing. The second Yu-Gi-Oh! anime has less death and violence and more card games, albeit with lives and the fate of the world at stake, and characters still die in backstory. Yu-Gi-Oh! The Dark Side of Dimensions, though manga-based, has characters sent to other dimensions and bloodlessly attacked by shadows.
Yu-Gi-Oh! GX was more upbeat than the original series, at least until season three began.
Yu-Gi-Oh! 5D's, which had a gritty apocalypse story, was followed by Yu Gi Oh Zexal, which is a much more optimistic series with a space-age theme and more focus on comedy.