Relative, family member, or longtime friend of a character who is "blind" to their actions.
If this is a heroic character or someone designed to impress, the sibling — especially if they're older — is hypercritical and only think of them as the doofy kid who wet the bed till they were 10. Conversely, a lame character will be liked for their hidden good qualities due to their close and protective relationship with the sibling. In this case, there's major overlap with being a Fan of Underdog.
Sometimes it's a fan instead of an actual sibling, and a chain is made where The Hero is a fan of a more famous hero, and the fan of The Hero sees them the same way but won't acknowledge The Hero acts like a dork most of the time.
- In Love Hina, Kanako's fond memories of her stepbrother, Keitaro, makes her somewhat oblivious to his failures. But maybe sympathy, among other things clouds her judgement.
- s-CRY-ed has the reverse situation, where Kanami seems oblivious to Kazuma's powerful Alter abilities and sees him as a kind-hearted layabout. It's later shown that Kazuma intentionally acts uncharacteristically pathetic around Kanami to encourage her to be more independent, apparently so that she'll have an easier time coping if the male half of their two-member family were to die violently.
- In Death Note, Sayu Yagami never finds out that her brother is really Kira.
- Yuzu in Bleach is similarly oblivious to her brother's powerful abilities and the supernatural activities and entities that surround them. This is most likely due to her faint spiritual awareness, especially in comparison to her sister Karin, who knows all about what Ichigo is and does, eventually confronting him about it in the Arrancar arc.
- Both of Chitose's "adopted" sisters in Happy Lesson frequently handwave their brother's grouchy outbursts.
- Subverted in Strawberry Marshmallow: Chika has no illusions about her elder sister Nobue. Still, the trope applies, as Nobue is the Cool Big Sis to all four girls regardless.
- Likewise subverted in Airmaster, where Maki's little sister, unlike everyone else, describes her as a huge clumsy ogre who gets stupider each time they meet.
- Inverted in Kamichu!. Shoukichi is the only one that seems to realize just how weird everything is, including the cat's possession.
- Mokuba Kaiba (Yu-Gi-Oh!) is absolutely devoted to his older brother, Seto. Indeed, he is the only regular character who calls Seto by his first name in the dub (in the Japanese, he calls him "nii-sama").
- Shuuichi, the little stepbrother of Kurama in Yu Yu Hakusho, is completely oblivious to his brother's demonic heritage and supernatural activities. He's also presumably oblivious to the fact that he has a demon inside his body that can possess him, or that he's being used as a hostage to keep Kurama in line.
- Pop Harukaze from Ojamajo Doremi, at least for the first half of season 1. Once she becomes an Ojamajo herself she subverts the trope both in regards of what's going on and later on, her relationship with Doremi.
- Carole Amherst, in Mutant Ninja Turtles Gaiden, thinks that her brother's funeral was staged and he's now become an actor who plays the role of a mutant turtle studying with fellow actor Raphael. If you think that's oblivious, read chapter six of the comic.
- In Sekirei, the younger sibling is also a part of the plan, but doesn't know of her brother's involvement in it.
- Inverted and subverted in Deadman Wonderland; Yoh, the apparently oblivious older sibling, reveals he's known about his little sister Minatsuki's Cute and Psycho tendencies all along, but wants to protect her anyway.
- In One Piece, the older brother Ace is horrified and angry when Luffy goes to Impel Down to rescue him because he believes that Luffy's just being the typical reckless, idiotic younger brother that he remembers that always made him worry. In an interesting inversion, Luffy himself at first doesn't want to go to rescue his big brother after discovering his life is in danger via his burning Vivre Card and explains that his older brother is strong and wouldn't appreciate being rescued (it's also pointed out that if the person in danger gets out of danger, their Vivre Card returns to normal). It's only when he discovers that Ace is on death row that he decides to go rescue his brother.
- Nunnally in Code Geass missed that whole bit about her brother being The Strategist for La Résistance during all those times when he was cutting class. Justified, since he goes out of his way to hide it from her and her Ill Girl status (including the fact she's blind) means it's very difficult for her to investigate. Although, the fact that she is very good at recognizing voices (being blind) yet does not recognize Zero's voice as her brother's despite the digital distortion being very slight does make her fairly oblivious.
- Eve from Baccano! is completely convinced that her big brother Dallas is a good person, despite increasing evidence otherwise.
- Sasuke from Naruto is unaware that Itachi killed his clan due to their planned coup d'etat so that the Hidden Leaf could be safe. When he found out, he did not take it very well.
- Yukina in Yu Yu Hakusho doesn't know Hiei is her older twin brother.
- In Frozen, Anna is convinced her seemingly-evil older sister Elsa is just misunderstood, remembering how close the two of them used to be when young, even when Elsa ends up looking really bad after seemingly ignoring Anna for most of their childhood, shooting ice spikes at Anna in the middle of an argument, and then promptly fleeing the kingdom, leaving the country in a magical blizzard in July. She turns out to be right - most of the issues really are misunderstandings or even accidents.
- Parodied in Johnny Dangerously when at one point the Pope (Dom De Luise) reminds all the neighborhood residents that Johnny's mom and brother think he's just a nightclub owner and not the notorious gangster Johnny Dangerously, and to keep the secret from them.
- Reuben of Little Odessa knew about his brother's shady dealings, but apparently managed to put it out of his mind for most of the time and still looked up to him.
- Tella sometimes appears to be this in Caraval.
- The Dresden Files: Harry Dresden played this once in the novella Backup. It's told from the point of view of Thomas, Harry's older brother. A woman hires Harry to find a kidnapped child, pressing two of Harry's Berserk Buttons. What Harry doesn't know is that the woman is a bad guy manipulating him into finding a book of rituals, that Harry will find with the child, and when he hands it over to the White Council, mass-producing the book will increase it's evil power, not diffuse it. Thomas, who can't tell this to Harry because of that very reason, has to pull all sorts of stunts to get things to work out okay, including letting Harry beat him up.
- Lyle Bennet on Heroes was pretty good about this for a while. Then he found out and ran away from the discovery. Then he got over it and became somewhat competent.
- Gioffre of The Borgias doesn't seem to take any notice of the corrupt political world the rest of his family are embroiled in.
- Supernatural: Even though Dean defines "morally shady," Sam is emphatic that he's more than a killer or a grunt and that he has looked up to Dean his entire life. He lets Dean take the lead in most aspects of their lives, trusts him absolutely (up until Season 9...) and craves Dean's approval. Sam's been shown to go a bit unhinged when he believes Dean has rejected him or that he's disappointed Dean, even though Sam is often Dean's Morality Chain and keeps Dean's most destructive tendencies at bay. Bear in mind that other characters' descriptions of Dean include "two steps away from being a serial killer."
- It's been noticed that the normally intelligent and perceptive Sam has been remarkably slow on the uptake as to how the MOC/First Blade are affecting his brother through Season 9, mostly just glancing worriedly at Dean and gently broaching the topic on a few occasions. Word of God has suggested that when Sam found out about the MOC, he just kind of assumed Dean knew what he was doing and could handle it, and it's taken quite some time for Sam to fully grasp that neither of those things are true. There have been other factors at play as well, including a major rift between the brothers, but part of the issue seems to be that it hadn't occurred to Sam (who has often fought internal supernatural forces throughout the series) that Dean could be vulnerable to similar internal forces.
- In Episode 1 of Life Is Strange 2, Daniel seems to buy his older brother's lie about them being on a camping trip, when in actuality, they are fleeing from the law. He finds out the truth at the end of the episode.
- Subverted with Gaz on Invader Zim: she is perfectly aware that her older brother Dib is trying to thwart an alien invasion, she just doesn't care.
- In Recess, Vince considers his older brother, Chad, to be the epitome of coolness, and is thus shocked when his friends reveal that he's a Hollywood Nerd.