A lot of the time i find that Tsundere's (or attempts at them) are far, far too mean or act this way for no real reason beyond fitting the archetype. Nagatoro is a good example of what im talking about, and in other cases a character is wrongly labeled a tsundere (Asuka from evangelion).
Toph Beifong: Avatar the Last Airbender
Toph is, by a country mile, the meanest member of her team. She's stubborn, sarcastic, and in classic tsundere style, can never really spit out her feelings. Despite her constant rude behavior and her inferiority complex, she is consistently loyal and honorable. Notably, unlike the rest of the Gaang, she has the least personal stake in actually ending the war. Aang, Katara, Sokka and Zuko all have familial ties binding them to the conflict, while Toph's motivation is largely the selfish (in a good way) desire to self actualize and prove herself more than her disability.
Her more difficult behavior is all coming from a place of needing to be taken seriously, and distancing herself from the image of being a vulnerable little doll her parents have of her. she's been coddled her entire life despite her being (at the time) tied for the greatest earthbender in the world. Her most defining moment of moral fiber, at least in my opinion, is during an event in which she and Appa--the groups flying bison and Aang's beloved pet, remain aboveground so that Toph can keep an underground library from collapsing on the group.
During this time, poachers attack the pair with the intent of kidnapping Appa. Toph responds by trying her absolute heart out to fight them off with TWO handicaps. First, shes spending an immense amount of effort protecting the library, and second, she's standing on sand, thus disrupting her Tremorsense abilities and rendering her even more blind than usual. Protecting both is clearly impossible, but she still digs her heels in and fights until it becomes clear that in order to save Appa she'd have to drop the library. She has to let him go, and spends a large chunk of the following episodes trying to atone for something that wasnt even her fault to begin with.
Toph is a fairly static character, but even she gets growth revolving around her learning to both rely on others and view her own internal strength in a heroic light... still picks on Sokka because she likes him though.
As a final tidbit, when describing one of her kid's fathers in the sequel series, Toph only offers him praise--specifically for his kindness, and the other male characters she crushes on she does so largely because they're kind as well. Despite her struggles to act on it herself, she values kindness (so long as its not condescending) incredibly highly.
Natsuki: Doki Doki Literature Club
Natsuki is first introduced as a stereotypical tsundere. She cant spit out anything nice without getting embarrassed, calls people mean names she clearly doesnt mean, and is all around kind of rude to the unnamed player character. Similar to toph, a lot of this comes from a place of being seen as childish and patronized. Her more simplistic style of poetry (i personally think shes the best poet in the group but i digress) and perceivably childish love of manga have left her very insecure. On a much darker note, her father is abusive and regularly starves her, resulting in her being underweight and (its implied) having a delayed puberty as well, so she looks even younger than she is.
Alongside her desire to be taken seriously, Natsuki heavily values authenticity and sincerity in how she and others present themselves... and the PC is lying about his intentions in joining the club--which Natsuki suspects. He's there to hang out with cute girls and possibly find a girlfriend, and any rudeness she shows to him beyond her baseline insecurity is completely justified.
Despite this, Natsuki is the most authentic member of the group, and is actually incredibly reasonable. As Monika (who is insane for plot reasons) gradually drives the other two girls, Sayori and Yuri increasingly insane by cranking up the dial on their worst traits (Sayori's clinical depression and Yuri's obsessiveness and inclination towards self harm), Natsuki remains relatively stable. She becomes far more cruel in her comments and insults, but even at the group's absolute worst, she desperately pleads with the PC--who she doesnt even trust--to do whatever he can to help Yuri, who at this point has been told Natsuki to off herself to her face. Even when Yuri is at her most hostile and Monika is acting like a psychopath, Natsuki is empathetic enough to know that this isnt who either of them are and that they need help--which displays a staggering amount of maturity from the character who initially seemed the least mature.
Si: Arknights Endfield
Si is effectively an immortal demigod... who happens to be only "well over a century" years old, making her the youngest of her kind by a longshot. the 13th of 12 (dont ask) VERY old siblings, Si is in a very weird place. She's described as a weird mix of a bratty teen and a cranky old lady, which makes a lot of sense in context.
See, Si is too told and too powerful to connect with most normal people, as anyone her mental age will grow out of it almost immediately, and she's already outlived many of her friends. She's also too young to truly relate and connect with other immortals, including her siblings who left her largely to her own devices, leaving her feeling incredibly lonely.
Her Tsundere tendencies come from feeling the need to present herself as a benevolent deific figure, while also having a very, VERY strong need for companionship that is going completely unmet. This combo means she often acts like she's stern and disappointed, demanding others be sufficiently courteous as befitting her station while instantly crumbling the nanosecond she actually upsets anyone she cares about... or suspects she did... or is anxious they might leave.
In terms of the player character, the Endmin, they are the one real connection she has. The Endmin often overexerts themselves, leading to them being in a medical coma for long periods of time, meaning the endmin is the closest in age and lived experience to her. theyre both deified figures who are seen as living legends, while still being people who put their connections with others as a primary motivator.
Well... the last said medical coma left Endmin with amnesia, so theyve completely forgotten Si. Whoops. She's obviously very hurt by this, even if she knows its not really our fault. She still voluntarily helps everyone that asks (and a lot of the time she beats them to the punch) and her little mini arc in 1.6 focuses on her taking the Endmin through a sort of spirit-quest (its complicated) to cure a spiritual wound they suffered. The entire time she is manipulative and dishonest, trying to get the Endmin to abandon their quest.
Her motivation for doing so is twofold. First, this quest poses a genuine threat to her friend's wellbeing (the equivalent of running a diagnostic on them nearly fucking kills the Endmin), but also because... well... we fucking asked her to. This entire quest was Pre-amnesia Endmins idea as both a test of your resolve, and as a chance for you to choose a different path if this wasnt what you wanted.
Si didnt want to put you through this, but does so anyways because both past and present you insist on it.
Even outside of the arc, all of her interactions have her being mildly rude or annoying at worst, and reading between the lines on basically... anything she says to you translates as "You're really important to me; i'm still important to you, right?"
When another character offers his assistance in your quest, she rudely brushes him off despite him approaching with perfect etiquette, writing him off as an "unnecessary nuisance" using even a single synapse will decipher that what she really means is "he's interrupting my time with you."
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Si's honestly probably my favorite example of a Tsundere because i never once felt like she went too far or was being that way for no reason. She's an awful liar so no matter what she actually says, the player can always see through her like freshly cleaned glass. It keeps her in the territory the game wants her to be in (endearing). obviously everyone measures these things differently but i found her adorable
