In the manga and OVA, Ryoko has very idealistic ideas about love, and seems to think that she is in a romance story instead of a war story. In the manga, even abandonment and heartbreak at the hands of her absentee boyfriend does not dent her idealism.
Rishar Vashtal from the manga also qualifies. He has romantic visions of a democratic Asran and genuinely wants to empower the Asranian people. Mickey, however, warns him that the Asranian people may call for his death after the war.
Akari from ARIA is a special case, in that she manages to stand out in a setting that is practically paradise incarnated.
The neo-nazi band. Having no real experience with the way the criminal underworld works, they're sent on a fixed race to "test their ability" against the protagonists, where they overspend resources, repeatedly underestimate the crew of the Lagoon, refuse to see facts, and waste time making dramatic and hammy proclamations about their heroic destiny as champions of the white race. Revy and Dutch kill all of them, and their would-be patron abandons them the moment it's obvious to him they've failed (though not before admitting to the leader that he set them up in the first place).
Rock also struggles with this in earlier arcs: His attempts to understand Revy makes her angry at him, trying to "save" Gretel failed utterly, and his attempt towards Yukio backfires completely. It isn't until "Le Baile de la Muerte" he starts to understand that if he wants to save people he'll have to become a cynical rotten power-player like Chang and Balalaika.
Both Suzaku Kururugi and Princess Euphemia Li Britannia from Code Geass genuinely believe they'll be able to reform the shockingly racist Britannian Empire and be facilitators for the peaceful integration of the Japanese people into the empire's fold. Cue Diabolus ex Machina on a national scale. This is subverted in the second season, where Suzaku forms a reasonable, if rather myopic, plan to free Japan (the rest of the world isn't his concern) and begins suffering from a bad case of Motive Decay until he realizes his ideals are nothing but smoke.
This is spoofed in official side comics, where Suzaku and Euphy are portrayed as so blindingly naive that they still believe in the Delivery Stork and Cabbage Patch Babies, while Lelouch looks on in stunned disbelief.
This trope is lampshaded artistically with Shirley, who has literally the largest eyes in the whole cast, with Euphemia just in second place.
Ichiro Yamada from the manga Freesia. He very much initially thinks that he can help the country by punishing ex-convicts and such, until he realizes quickly that the Vengeance Proxy Enforcer firm that he works for is nothing more than a group of contract killers for people who have massive grudges.
In the manga version, Scar's brother and the Rockbell family are wide-eyed idealists who believe in the basic good nature of man. The Rockbells leave their practice so they can heal the Ishvalans being massacred by the Amestris army, and Scar's brother wants to learn alchemy so that he can better understand the bonds of humanity. During an attack Scar's family is killed, and Scar's brother tries to shield Scar, but is unsuccessful, and Scar loses his arm. Scar's brother sacrifices an arm and his life to save Scar, and Scar wakes up in the Rockbell's hospital. Finding out that his brother's arm is now attached to him causes Scar to go temporarily insane, and he kills the Rockbells in a Freak Out.
Roy Mustang is the other side of the coin. His sometimes borderline dumb faith in human nature helps him sometimes (when he took for granted Dr Knox would cover his scheme to save Maria Ross, because they were war buddies) and other times dooms him (when he believed overthrowing the Fuhrer would be a piece of cake when people found out he was a Homunculus. It turned out the brass knew and couldn't care less). Still, his idealism is precisely what makes his subordinates so loyal to him.
Havoc: He's stupid! How can such a naive thing keep climbing up in this country? Hawkeye: I think it's good that there are idiots like that, once in a while.
The first anime, on the other hand, makes a point of contrasting Al's childlike optimism and naivete with Ed's growing cynicism and the horrible truths of the world aroung them.
Galaxy Fraulein Yuna: Yuna Kagurazaka is one of the rare examples of this trope not to suffer either of the standard fates.
Albert from Gankutsuou, along with having Horrible Judge of Character. He is undoubtedly the most naive and idealistic of all the characters in that series. He truly believed for a long time that his friends' (and his own) families were perfectly rosy, and that the Count is a wonderful person. (He was very wrong, by the way - they were all insanely messed up.) Not to mention how he manages to go on about "true love". However, despite all hardships he goes through, Albert ends up taking the route A and becomes a better person who not only saves the Count's soul from Gankutsuou but also fixes his father's wrongs by becoming an envoy of peace.
Great Teacher Onizuka: Minami Kikukawa is a training teacher who would love teaching in a private school because in a public school she would have got to deal with troubles such like bad students and administrative corruption. Fuyutsuki quickly warns her that she is Tempting Fate with that naive attitude. After meeting the class four students (who prior Onizuka's arrival and lessons hated all adults and tried to drive all teachers crazy or suicidal), she realizes things are not so simple.
Arguably, Éclair from Kiddy Grade, who, despite having dealt with the dreadful realities of GOTT and galatic politics for many, many years, has somehow avoided becoming a cynic, and actually keeps up her spirit to fight for her ideals. Granted, this may be due to two things: (1) she does use autohypnotic suggestions to block out some of her memories temporarily, and (2) as a superhero, and with her partner, she does in fact have the ability to back up those ideals with with force.
Kanzaki Nao in Liar Game. Almost every chapter. You'd think that one of these days she'd learn... Except you know, she's usually proven right by the end.
Negi of Mahou Sensei Negima! starts out as one of these, but he eventually starts to realize that good and bad aren't quite as clear cut as he thought they were. Evangeline actually deliberately discourages his idealism (despite the fact that she's a Noble Demon who's constantly sliding towards Anti-Villain territory). Negi eventually admits that he can't always be the good guy, although he still tries to go with most "good" option available.
UC Mobile Suit Gundam, have at least one pacifist who thinks they could stop the fighting, usually they are proven wrong and lives to watch the ramifications of their actions.
Tenma and Nina from Monster, despite being frequently subjected to horrific trauma. The fact that Tenma in particular absolutely refuses to become cynical about the human race drops him straight into Badass Pacifist territory.
Played With in Princess Tutu. Duck Jumped at the Call to help Mytho regain his heart, never stopping to consider that he might have had a very good reason to shatter his heart. Her idealism slowly wears off throughout the series as she discovers how her thoughtless actions keep changing things for the worse. However, her initial optimism does have an affect on Fakir, who eventually returns the favor by giving her hope when she's on the brink of a Despair Event Horizon.
This is what makes Alice L. Malvin of Pumpkin Scissors stand out from many of the other nobles of the setting. She firmly believes in her cause to "eradicate evil" and that others will push for it too. This is what got Machis and Oland to join in the first place.
The title character of Revolutionary Girl Utena, which can be infuriating when you realize that she refuses to see the emotional hardships that her peers go through (Juri's conflict over Shiori and her sexuality in general come to mind; Utena brushes it off and tells her to stop acting cold). Miki is this to a lesser extent, in regards to his sister Kozue, but it may be more that he's a genuine Nice Guy more than anything else.
Rurouni Kenshin Himura is a good example of this trope. Some might consider him Incorruptible Pure Pureness, but oldhabits die hard... Except his intro speech at the end of the first chapter goes, "no, swordsmanship is an art of killing. Kaoru-dono believes a sweet, naive lie. But if this one had a wish... it would be that her sweet lie would become the truth of this world." Kenshin's Walking the Earth with Obfuscating Stupidity routine involves some serious ideals, but despite avoiding his battle expression most of the time he's not too wide-eyed. He's got the world-weary thing going, but values Kaoru as a Wide-Eyed Idealist. Some of the stupidity probably isn't fake. The line is impossible to find, as is common with Crouching Moron, Hidden Badass types. His backstory involves a bit of this, despite all his childhood trauma—it caused him to wind up a sworn assassin in a civil war.
Sayonara, Zetsubou-Sensei: Kafuka takes this trope and runs with it. Everything has a good side to her: a Trash Can is a "Treasure Chest for the Homeless" and it only gets worse from there.
The anime-exclusive character Filia, the Golden Dragon, is this combined with Holier Than Thou taken to aggravating levels. It doesn't help that she was sheltered for most of her life, but even after she learning the Awful Truth, during the last battle she believes that the Big Bad isn't beyond salvation (it's established clearly that he is at that point) and doesn't want to destroy him, even as he's consuming the world at that moment...
Vash The Stampede is determined to be one. No matter what he sees, what humans or Knives or anybody do, to him or anyone. His traumas are simultaneously cases of Break the Cutie and Break the Badass, and are usually horrific. Worse in the manga, where he is clearly fighting to maintain his idealism over his own common sense and has a lot more bleak moments. The setting is also much darker, since the series went seinen after the Fifth Moon. But he always stands up again. Because he won't give up on humanity and by extension Rem. And on himself. After all, if he gives up on people then what does he have to resist Knives' Hannibal Lectures with, and what have all these years meant? Therefore, Technical Pacifist willing to Turn the Other Cheek to a sometimes absurd degree. Vash is helped by his own awesomeness; when Knives and his subordinated aren't involved he can usually pull a casualty-free resolution out of the worst situations imaginable. Sure, this has meant horrific scars all over his body, but it gives him all kinds of warm fuzzies and hope. He wants Wolfwood to see this. Wolfwood wants him to see that most people are only human and you can't save everybody all the time.
Know who's the Trigun poster child for this trope? Manga Knives. He was all "our hearts are the same as people's, I'm sure if we try we can understand one another," and actually cried when the first human they met besides Rem accepted them. Then he Went Mad From The Revelation that Humans Are Bastards, and resolved to Kill 'em All.
Meryl is a little naive but never an idealist. Millie is... strange. Maybe a wide-eyed idealist. Maybe just terminally clueless. Actually very sharp under it all, and very tough. Anime Millie is Wolfwood's other foil, and they become a couple. One of Wolfwood's Character Development soliloquies involves the frustrated observation that Millie and Vash always "do everything I can't, like it's no big deal."
Steve in Gilbert Hernandez's "Love and Rockets X" story within Love And Rockets.
Tomcat in the Jedi vs. Sith. He believes everything he hears in the songs and stories that claim the Jedi are invincible heroes. When he ends up in the middle of the battle against the Sith and sees Jedi dying in the mud with their non-Force sensitive comrades, it does not end well.
Due to the way comic books have been since the end of the Silver Age, characters and stories have gone from escapism to complex story telling, usually in the form of being Cynical and Darker and Edgier types. Because of this, any hero who hasn't done so becomes this by default. Examples include:
Superman. Even in the face of unquestionably dark odds, he still stands by his beliefs and ideals. He fully admits that the world isn't perfect, so he's not stupid, but he tries his damnest to make it better.
Similar to the above, Spider-Man. While he's got a very misplaced reputation for being whiney and angsty (coming from the second two Raimi films playing up his Woobie points and the nineties being, well, the nineties), Peter Parker's main reason for being so popular isn't because of his powers, but because he'll always do the right thing, no matter what theworld throws at him.
Robin. All of them, except Damian, which plays against Batman's seriousness and the grimminess of Gotham. Dick stayed happy and upbeat after his parents died in front of him and became the Boy Wonder, Jason too, until the world broke him in A Death In The Family and broke him again in Under The Hood, Tim's entire reasoning for becoming Robin was that Batman needed one to keep him off the edge, and Stephanie's entire MO is to stay upbeat about everything even in the worst situation. Barbara too, though that shattered after The Killing Joke.
Saori Tagawa from The Ikaris is a marriage counselor who boasts she has NEVER failed on saving a marriage. She also has a very idealistic outlook about love and marriage. Attempts to talk her out of it are met with a Shut Up, Hannibal! sharp retort.
Téa from Ultimate Re Imaginings, right to the point of trying to brush off Joey's claims that his father was abusive, all the while he was sitting in a hospital bed.
Vale, the heroine of the Hunger Games fanfiction Some Semblance of Meaning, has a prominent idealistic streak. Back in her home district, she used to make up stories full of idealism, and even in the midst of the Hunger Games, she desperately wants to believe that there is good in everyone (despite what the "pragmaticvoice" in her mind says). She undergoes quite a bit of Break the Cutie but never gives up her belief in the underlying potential for good in humanity. She eventually dies defying the Capitol in the hopes that it will prove a point to those watching, and in fact, this action does plant the seeds for the rebellion that occurs thirty years later in Hunger Games canon.
Another example: District One's Obsidian is quite idealistic for a Career. For example: "Growing up and hearing stories of Hunger Games past, they had seemed like so much fun, adventures with fantastic, unimaginable riches and eternal fame as the victor's reward. A dream come true for a small, idealistic boy with a 'bright' future as a Career tribute lying ahead of him." However, in the arena, he experiences some Break the Haughty when the brutality of the Games come into conflict with his expectations and beliefs. He ends up winning the Games after Vale's death, but as a very broken shadow of the carefree Career he once was.
Renate Richter in Iron Sky thinks that all Hitler wanted was peace under his gentle rule. It's clear that she's been brainwashed by the Moon Nazis, and the film starts with her doing plenty of brainwashing of her own of young Nazi children, showing them a 10-minute version of Charlie Chaplin's The Great Dictator. Her idea of romance is to be genetically compatible with an Aryan man to produce perfect children. After arriving to Earth with her "fiané" Klaus Adler (who has no such ideals and merely wants to conquer the world), she helps the President's re-election campaign by writing inspiring speeches straight out of Hitler's handbook (with gems like "we raise our hand to one nation"). She tries to convince James Washington (a black male model who was "albinized" by Renate's Mad Scientist father) of the Nazis' good intentions by showing him The Great Dictator, not realizing that it's the full 2-hour version. Her illusion finally breaks after seeing the film and a disastrous encounter with some skinheads spray-painting her "symbol of peace" everywhere.
In Mr. Smith Goes To Washington, all Mr. Smith wants is a Boy Scout camp and nature preserve on a piece of land. Too bad the rest of the Senate is against him.
Otto from One, Two, Three about Communism. He even thinks it's a capitalist lie that Siberia is cold, and is happy that the Communists assigned them "a magnificent apartment, just a short walk from the bathroom!"
Horrendously deconstructed in Europa by Lars von Trier: Leopold Kessler, a naive German-America pacifist arrives to post-WII Germany to help his compatriots survive aftermath of the war. He is repeadetly bullied and resented by his own uncle, gets involved in intrigues between American military and Nazi resistance, the woman he loves and eventually marries turns out to be a member of Werwolf, he, betrayed and used by veryone, finally snaps and blows the train with himself and everyone else in the movie, and drowns. What is worth noting, that train was the one he just saved from being blowed up by The Remnant - and nobody is grateful to him.
Will Proudfoot in Son of Rambow in spite of having lost his father and being raised in a repressively conservative religious household.
While Charles Xavier in X-Men: First Class isn't exactly naive, he still has an extremely idealistic attitude towards Mutant/Human relations. Even when the humans turn on the X-Men in fear, he still continues to beieve that the mutants should try to be the better men, in the hope that they will someday be accepted.
Sansa Stark, who bases her whole life around singers' tales, is a perfect little lady, gentle and trusting. Until the person she is starry-eyed over cuts off her father's head in front of her.And then MUCHmisfortune followed.
Less drastic but still quite there examples also exist with her siblings: her younger brother Bran especially, who believed in the same songs and stories as she did. His Break the Cutie process just happened faster.
The young baby-faced soldier boy in All Quiet on the Western Front definitely qualifies. as should be completely obvious given the nature of the book and this page, he dies.
Voltaire's Candide. Among many, many other examples in the book is Dr. Pangloss's thoughts on having caught syphilis, and having had an eye and an ear removed as part of the treatment:
"O sage Pangloss," cried Candide, "what a strange genealogy is this! Is not the devil the root of it?" "Not at all," replied the great man, "it was a thing unavoidable, a necessary ingredient in the best of worlds; for if Columbus had not caught in an island in America this disease, which contaminates the source of generation, and frequently impedes propagation itself, and is evidently opposed to the great end of nature, we should have had neither chocolate nor cochineal."
Cosima from Comrade Death. She flat out refuses to see Sarek for what he really is. He confesses to abandoning her husband to die, and later refuses to save her grandson from going to war, and both times she dismisses his spite as being concealed guilt and claims he would have helped if it had been in his power to do so.
Tyentyetnikov starts as this in Dead Souls, tries to improve the lot of his serfs, with at best mixed results, and becomes apathetic in the end.
Subverted by Carrot Ironfoundersson. He starts out as a wide-eyed idealist... except that for some reason, his idealism somehow works. He can talk anyone into behaving like a friendly, reasonable person. If any other character tried it, they'd be dead. It works because he's big, strong, usually accompanied by city watchmen (including a troll and later a golem) and, most important of all, is fairly intelligent. Carrot is an actual idealist, rather than just naive like most of the examples here; he knows full well that Humans Are Bastards and simply refuses to be one himself. Also, the world does tend to warp itself around him. After all he may or may not be the heir to the throne of Ankh-Morpork, and in a world chock full of narrativium, how can things not go his way.
In The Colour of Magic and The Light Fantastic, Twoflower, if anything, has an even more rose-tinted view of the world, to the endless irritation of his traveling companion Rincewind — and likewise comes to no harm. Admittedly, this is probably because he travels with a Cosmic Plaything, so all of the trouble they run into goes after Rincewind rather than him. After they part ways, he does get thrown in a dungeon to rot for being so wide-eyed, which supports that theory.
Isherwood Williams in Earth Abides, although he's not a complete naïf.
For Want of a Nail features a nation full of politicians like this in the Confederacy of North America, a nation formed after the British Empire restructured their management of their colonies following the American Revolution.
In a twisted way, Inspector Javert of Les Misérables. He might be a snarky hardass, but he has absolute faith in authority and the law, believing that no judge or politician has ever erred, that leaders can all be counted upon to have nothing but the public good in mind, and that whoever has met the harsh punishments of the justice system therefore deserves it. This runs up hard against the story's Full Spectrum Morality, with fatal results.
In Outbound Flight, the smuggler Maris Ferasi fit this trope pretty well. She had the utmost trust in and adoration for the Chiss commander Thrawn. Unusually, she wasn't disillusioned within the book — Thrawn lied about what he had done to resolve an extraordinarily prickly conflict, letting her leave without knowing just how much of a Downer Ending the whole issue became. Why?
Thrawn: There are all too few idealists in this universe, Car'das. Too few people who strive always to see only the good in others. I wouldn't want to be responsible for crushing even one of them. Car'das: And besides, you rather liked all that unquestioning adulation coming your way? Thrawn: All beings appreciate such admiration.
Jane Bennet of Jane Austen's Pride and Prejudice. Her younger, more cynical sister, Elizabeth, is convinced that Jane's new friend, Caroline Bingley, deliberately sabotaged her romance with Caroline's brother in order to hook him up with the sister of his best friend Darcy — all to increase Caroline's own chance of getting hitched to said best friend. Jane remains convinced that Caroline is her affectionate friend and would never do anything to hurt anyone, and more importantly, never do anything less than beneficial to her brother's happiness. Obviously he must prefer Georgiana... It takes a surprise face-to-face meeting with Caroline for Jane to admit Elizabeth was right about her, but she displays the same naivete and belief in love and the innate goodness of man when Wickham seduces their youngest sister, Lydia—despite Jane and Elizabeth knowing that he's tried the same technique on at least two other girls.
Moomin-"all I want is to grow potatoes and live in peace"-troll of The Moomins.
Toglio in Norman Mailer's The Naked and the Dead. Always thinking to himself about how he and his squad are "The good ol' boys", hard-working and patriotic. Then, of course, he gets his leg shot up to hell and sent home.
"Alone of us all, Rinaldo has no personal ambition. He sees in Conan a red-handed, rough-footed barbarian who came out of the north to plunder a civilized land. He idealizes the king whom Conan killed to get the crown, remembering only that he occasionally patronized the arts, and forgetting the evils of his reign, and he is making the people forget. Already they openly sing The Lament for the King in which Rinaldo lauds the sainted villain and denounces Conan as 'that black-hearted savage from the abyss.' Conan laughs, but the people snarl." "Why does he hate Conan?" "Poets always hate those in power. To them perfection is always just behind the last corner, or beyond the next. They escape the present in dreams of the past and future. Rinaldo is a flaming torch of idealism, rising, as he thinks, to overthrow a tyrant and liberate the people."
Twenty Thousand Leagues Under the Sea: The Professor Aronnax must be constantly reminded that other people are not as good as himself. He really doesn’t want to believe that Nemo is doing something sinister, and Ned Land must remind him that the war ship that is shooting the Nautilus is doing it on purpose.
God-King Susebron from Warbreaker. His entire experience of life outside his palace consists of having been read a book of fairy tales by his mother as a child. Semi-subverted in that while he does develop a more realistic view of the world, he never loses his almost childlike sense of straightforward goodness.
Lieutenant George in Blackadder Goes Forth, despite having spent three years in the trenches of World War I, is still mindlessly optimistic about giving the Germans a good bashing, and readily believes all war propaganda to be true. The grim reality of his situation (in particular, the event of "going over the top" he's been looking forward to for all the series) dawns on him when he realises that he's the only one of his class group left, all the rest having been killed. He goes over the top shortly afterwards in a Bolivian Army Ending. His response to realizing all his friends are dead is "Well, I guess I'm the only one left... oh.... I mean, if it wasn't for the excitement of going over the top tomorrow, I might be a bit down!" Subverted when he says to Blackadder: "Captain, I'm... scared." Up until that point, it's not clear whether the whole thing was intended to be more of the show's black humor, or if it was actually supposed to be horrifying. That line cleared it right up. Then, it goes From Bad to Worse.
Annie in Community. She even thinks her nickname is "Irony-free Annie".
A.W. Merrick and Reverend Smith of Deadwood. Since they both live in Deadwood this doesn't work out too well for either of them. Reverend Smith's religious faith is seriously undermined when he develops a fatal brain tumor and must question the purpose of his suffering. Merrick gets off easier, he's able to hang on to his world view for most of the series but has to toughen up to deal with what life keeps throwing at him.
Dr. Molly Clock. Partially subverted, however, in that her incorrigible optimism is undaunted in the face of the naked cynicism of Dr. Cox and Dr. Kelso, and even allows her to triumph against them.
J.D. himself might fit too, at least at the beginning.
And then there's the one-episode character from season one (played by Sean Hayes), who is eternally optimistic about the chances of a little boy in his care, until finally he suffers a Heroic BSOD as he realizes nothing he's tried is working and the kid is going to die.
Star Trek: Deep Space Nine: Naive, gentle Tora Ziyal, despite growing up as a prisoner of the Breen, despite being rejected by Bajorans and Cardassians for her hybrid status, still remains trusting and hopeful that she can somehow help, with her art that resembles that of both cultures, in proving that the groups aren't so different after all. She knows her father, Dukat's past, but loves him anyway, sincerely believing he's changed, and keeps right on forgiving him. Too bad that choosing saving her friends over staying with her father gets her shot by her father's Dragon as a traitor. Dukat goes mad as a result.
To some extent, Data in Star Trek: The Next Generation. Not completely — he's good at being skeptical and savvy about more abstract situations — but has a tendency to be far too trusting and willing to get close to people who he knows personally or who behave in an well-meaning manner, usually resulting in injury and/or betrayal (e.g., Lore, Ira Graves, Ishara Yar, brainwashed members of the crew on various occasions). Considering he's an android, stereotyped as logical and dispassionate about things that could emotionally compromise normal people, this trait of his is almost a subversion. Or perhaps his programming isn't designed to pick up on "sketchy vibes".
Sam Seaborn in The West Wing. Often, he creates idealistic scenarios and goals that sound wonderful, but when he presents them to Leo or the President, they are shot down because of being impractical, a waste of time, or just plain dangerous. He also is very trusting and naive, which gets him into trouble on a frequent basis. Often, as in the case of a public education plan he developed that would have been revolutionary, he completely forgets to factor in a budget, accidentally assuming that there are no limitations. Ironically, this makes utter sense, as this seems to be the most glaring problem with entire American Dream.
Phil Coulson of Agents of S.H.I.E.L.D. and the Marvel Cinematic Universe is a very idealistic man who believes that people are fundamentally good. His belief in heroes is seen as slightly old-fashioned, but it's implied that this fandamental faith in human decency is why he's described as Nick Fury's "one good eye" and why Fury is willing to go to such lengths to resurrect him. He's rather like the Token Good Teammate for the rest of SHIELD and, in an interesting example of Playing with a Trope, his idealism seems to be highly valued by the more cynical agents he works for and with.
Billy Joel's song "Pressure" is about a Wide-Eyed Idealist and how unrealistic his hopes and expectations are.
In the backstory of the old BattleTech world, the last First Lord of the Star League, Richard Cameron was orphaned as a boy, and grew up with idealistic, Arthurian vision of his supposed role as head of the multi-kingdomed, federal empire. Since politics in the Battletech universe are much more realistic than that, he was the worst possible choice for the critical throne at the worst possible time, and catastrophe followed. Not helped by the fact that an Evil Chancellor, who would later go on to kill Richard and bring the Star League to ruin, was warping his mind and constantly clouding his judgment towards said idealism.
Leliana in Dragon Age: Origins is an inversion. While definitely cheerful and idealistic, she used to be much more cynical and manipulative in her role as a spy and assassin where she prided herself on her ability to "be the woman" her target was looking for in order to get close to them. Her current role as a lay sister in the chantry is her Becoming the Mask, although her old teacher would have you believe otherwise. As with Jade Empire, you can encourage her one way or the other.
Fenthick in Neverwinter Nights, so much that he cannot comprehend evil. Linu is a lesser example.
NPC rather than party member, but Dragon Age II has Seamus Dumar. He's an outspoken opponent of the unthinking fear the qunari in Kirkwall inspire, and believes in bringing the two sides closer together (no easy task, since qunari aren't that approachable themselves). Too bad he lives in a Wretched Hive and his father is a well-meaning Slave to PR. Mother Petrice has him murdered and tries to frame the qunari for it to spark a race war.
"Will / Ed" from Advance Wars: Days of Ruin / Dark Conflict. His idealism arguably pushes him dangerously close to being an Idiot Hero, as he is often wildly optimistic and consequently sometimes fails to look at situations properly. However, his will and sheer determination in even the worst of situations often leads to at least one crowning moment of heartwarming. Case in point — mission 16, which starts off with desperate music playing pushing ever closer to the Despair Event Horizon, when suddenly Will/Ed decides he's going to fight, and the music changes from desperate to sheer awesome.
In Deus Ex: Human Revolution, David Sarif is this to an extent. In a world of high tech cybernetics, ruthless conspiracy, corporate warfare, AndBad Weather — signs that would warn a Genre Savvy individual that s/he's in a Cyber Punk setting, Sarif believes that the best thing to do with augmentation technology is to remove all restrictions on it, and that doing so will help the people of the world. Of course, despite the multiple endings, this is a prequel to Deus Ex, so we know that all four endings will result in the exact same scenario a few decades down the line. His belief that merging man and machine will create a better world is vindicated by the best ending of Deus Ex when the hero merges with a benevolent AI.
Flonne in Disgaea falls under this trope. She never ceases to be an overoptimistic idealist who believes that demons can love, and that Seraph Lamington is a good guy. In the best ending she's absolutely right.
Tahlkora from Guild Wars: Nightfall. "I signed on for the heroic songs and the praise. I did not sign on for the blood-sucking bugs."
Anduin Wrynn from World of Warcraft displays the qualities associated with this trope. Despite the chaos in his past and his father's stubborn vehemence toward the Horde, Anduin firmly maintains that "both [his] people, and the Horde, are essentially good." His benevolence toward both the Alliance and the Horde is unchanged even by his near death at the hands of Garrosh Hellscream, the present Warchief of the Horde at the time.
It is even implied during a vision from the draenei prophet Velen that Anduin may lead the forces of Light during the final battle against the Burning Legion, placing him in direct contrast with Sargeras, who views the denizens of Azeroth- the Alliance and the Horde by extension- as corruptible and impure.
Poor Sigurd from Fire Emblem Jugdral. He charges into bandit territory to rescue his childhood friend, falls in love and marries a beautiful maiden, and some time later charges back into the fray to rescue another friend. Unfortunately, Augustria is way more political than Verdane and Sigurd's actions aren't seen as quite so heroic. And that's just the tip of the iceberg.
Komari from Little Busters, who always tries to look on the bright side, has a childish temperament, and hates sad stories. And then it turns out that this is because her brother, who was very sickly, tried to shield her from anything painful, only telling her happy stories. Even when he died, he convinced her that it was just a dream. While in good faith, this had terrible consequences - Komari repressed the sad memories, but they're triggered whenever she encounters death or blood, causing her to have a Heroic BSOD. The main development at the end of her route is her learning to take a more realistic approach and accept both the good and bad parts of life.
Franchesca "Kid" Martines from Angels 2200 is a textbook example. Not surprisingly, she almost gets booted off the squad when she can't bring herself to fire on an enemy fighter knowing she'd be taking someone else's life.
In El Goonish Shive, Grace is this in all things including nudity, and so was Susan before her Mercy Killof the aberration. Literally so — her eyes change into her current half-droopy state when she looks down at his corpse, and while she still haswideeyesquiteoften, they do tend towards the "half-droopy". After the encounter of a weird kind with Jerry led to Freak Out, though, she now tends to having wide open eyes more often than not.
Then there's Jake English, who considers Erisolsprite, a vile-tempered Jerkass of the first order, to be a "friendly guide" despite the sprite in question emphasising how much he hates Jake in every other sentence.
Lisa from Mechagical Girl Lisa ANT is one of these... only thing is, not only she still firmly believes her life is a Magical Girl anime despite all she's been through, but she doesn't even cares about her robot outfit being actually a Humongous Mecha for ants.
Seiko from Used Books is a great example. She is constantly standing up for people the others deem as villains. She holds fast that people are basically good, even if they have done nothing but cause hardship. She also stops in the middle of a battle to bandage up an enemy someone on her own team just injured.
A toned-down version of Penny in Dr. Horrible's Sing-Along Blog. "...a generally nice person whose idealistic attempts at solving the problems of their world turn out to go horribly horribly awry..." Do I detect a bit of irony?
Chris Davidson from v4 may indeed be this as well.
One could easily make a case for Carol Burke as well, who seems to genuinely believe they are going to be rescued and the terrorists wouldn't get away with it a fourth time. To her, very few at her school would actually play, especially her friends. Heck, she trusts ReikoIshida and gets killed for her troubles.
Orn "Dutchy" Ayers could also be interpreted as this. However, it's also a major reason why he's considered The Woobie; he's smart enough to know that although things should be good and he wants to do the right thing, things... aren't working out. As a result, he doesn't take things very well, and spends a good portion of his time on the island in a Heroic BSOD, wishing he could save all his friends.
Katara is this to some degree, at least in the earlier episodes. Her idealism is lampshaded by the portrayal of her by an actor in the Lampshade Extravaganza epsiode, The Ember Island Players:
"it just gave me so much hope...!"
Silverbolt of Beast Wars started out as a starry-eyed idealist. He was so thoroughly chivalrous that he refused to hit or fire upon a female (Blackarachnia) even if his own life, or the lives of his comrades, depended on it. His naivete took its toll in the three-part second season finale where he refused direct orders from Optimus to capture Blackarachnia, instead going after her to help her dig up the Ark. This enabled Megatron to make it to the Ark easier and gain the access codes from Blackarachnia after threatening Silverbolt's life. Then Megatron went into the Ark and fired a fatal blast into the still dormant Optimus Prime's head, triggering a cataclysmic time storm that nearly destroyed all the Maximals and wiped out time and space. All thanks to Silverbolt's refusal to capture Blackarachnia. Later on, of course, everything gets cleaned up but Silverbolt's actions nearly led to the destruction of time and space due to his wide-optical idealism. In Beast Machines, this trope becomes subverted as Silverbolt is transformed into the villainous Jetstorm. Blackarachnia does bring him back but once Silverbolt returns, he no longer has the rosy outlook on life that he used to, becoming a bitter Anti-Hero for the remainder of the series.
It should be noted that despite leading Megatron to the Ark the first time, his continued pursuit of Blackaracnia kept her on the Maximal side all through season 3 despite some close calls regarding her Chaotic Neutral yearnings. In fact, it's only because of his devotion that ultimately she becomes a real Maximal. This ironically is the only thing that saves the future yet again when she's the last maximal to survive a mental takeover of Optimus Primal, and thus she's able to save the ark from self destruction.
The Fantastic Racism of Manhattan is particularly painful for Angela of Gargoyles, who was raised on Avalon where humans and gargoyles live in harmony. She also hopes more than is wise or reasonable that her mother Demona can change or be redeemed.
Zeta from The Zeta Project is naive and kind, always taking people at their word, a terrible of judge of character who thinks the best of everyone and generally easily manipulated. It's due to being so young and having no knowledge of the world beforehand, and to be fair, his friends do try to help him get better about this.
In Transformers Prime, Optimus when he was Orion Pax as Megatron's protege in the Cybertron civil rights movement. He ended up endearing himself to the general public compared to his mentor's more ruthless methods.
Wally from the Where's Wally? cartoon series fits this trope to a T but manages to avoid the horrible death part. He's too cheery for his own good and his dog Woof has more common sense than he does yet he always escapes unscathed from his dangerous journeys.
In the early seasons of The Simpsons, Lisa started out as this, but as the series progressed, she became a Deadpan Snarker who has as much compassion as a housecat towards her own brother, and Homer from time to time.
Brattus and Mole from Mr Bogus both show shades of this in most of their appearances.