The main distinction to establish here is the difference between aesthetic personality and conscience. Aesthetic personality is shallow. It’s the surface of the person’s outer quality, how they act, not necessarily why; it’s about the “clothing” of their mind, how their actions look. Conscience is deeper. It’s the ideological motivation for a person’s action – hence why they act. While in actuality there is no (or at least shouldn’t be) causal link between the how and why of actions, anime – especially in the past few years – makes use of repeatedly played-out stereotypes and archetypes which have anchored onto the corpus of representation established by the rearticulation and recycling of character frameworks to signify a generalized type of person.
Now, using only two characters isn’t much of a cross sample, but the similarities here are, nevertheless, undeniable. Glasses. Black hair. Two-sided bangs. Pale. Coincided with stoic, reserved, intelligent, cunning. It’s important to note that they’re juxtaposed to more brawny characters. In terms of aesthetic personality, the archetypal brains/brawns duo is in itself a binary often utilized for cast expansion.
Possibly for a further touch of coincidence, there’s the role of the pseudo-helpless tag-along girl.
Of course the binary of brains/brawns isn’t the only one used, and necessarily there are exceptions. One might be a passive/aggressive combination.
In the DBZ universe, due to the relatively simplistic art style, everyone is inherently categorized within the same visual archetype: ripped as hell. The dire lack of differentiating body types leaves only visual clues such as hair (or lack thereof) and height to distinguish between aesthetic personalities and consciences.
Future Trunks first appears against a mechanized Frieza as our stoic, smooth voiced Eric Vale (who also voiced effeminate Yuki in Fruits Basket). While Trunks is in himself a sign, he retains qualities of aforementioned characters drawn from these anime artifacts as well as constituting meaning from juxtaposed representations vis-à-vis the other DBZ characters: the sword behind the back, while being a trait beholden to both Mugen and Ichigo to indicate GAR, here, it functions to distance Trunks from the others as, primarily, futuristic and exotic since it complements the fact that he actually is from the future. I wouldn’t say that Yajirobi counts here simply because he’s not a Z Warrior. (and his katakana[?] is worn on the side.)
Endlessly creating categories to justify exceptions isn’t logically digestible – as the visual ambiguity between Goten and a younger Goku attests to (is that supposed to mean anything? Doubtful, thus the irony of talking about things like causality) – but I think the examples here are concrete and within the limits of authorial predictability. For good measure, a counter example is the abundance of characters in LoGH that don’t readily conform to the previous visual norms but still demonstrate healthy amounts of GAR or similar aspects of aesthetic personality (LoGH is not without “flaws,” however).
While cultural artifacts – like swords – are deployed to complement the generalization of an archetype, these artifacts, signs in themselves, have no meaning until they enter the process of representation. Basically, the artifact needs the person to acquire concrete meaning – it is transitive. Until artifacts acquire a context, they are mostly floating signifiers, able to mean a large number of things, having no definite meaning.
Without context, glasses alone have no implicit meaning. What is the image supposed to mean? Nothing and everything. It can imply geeks, nerds, nerdom, otaku, intelligence, eyesight, ophthalmology, the looking glass, abstract psycho-sociological ideas. Hell, this specific image could be an artsy photograph if you wanted it to be. But then when you add the context…
I don’t think any of these depictions have much an effect on the character. They’re added for the occasion, the rhetoric of the character’s aesthetic personality. Cultural artifacts – we can probably consider them tropes in themselves – like glasses, are added as weapons to increase the rhetorical armament of the character’s superficiality. The character’s shallow aesthetic personality is subsequently able to attack directly the floating, unanchored conscience which the animator wishes to latch onto the concrete character. Without images, aesthetics, without stereotypes, archetypes, idiosyncrasies, the animator has an increasingly difficult time attempting to falsely justify the basis for a character’s actions. What if Sanae looked like this?
Surely, based on convention, her glasses don’t signify the same meaning as Sanae’s! But don’t fret too much about appearances, since hypothetically, a person that looks like this is totally capable of acting similarly to Sanae and on a identical ideological basis. This is the three-step establishment of visual and mental causality that animators develop in order to concretize recycled character archetypes:
visual appearance [signifies] personality [signifies] ideology
in other words…
cuteness [signifies] good-natured, loving, compassionate [signifies] human lives and emotions are paramount, motherhood is essential to the state of the family
Of course there are exceptions. Also take note of the girl from FLCL (since I don’t have any screenshots available and I don’t remember her name). In these exceptions, it’s much harder to discern the effect that glasses emphasize. In True Tears the glasses might be metaphorical – ie. attempting to say something not even about Hiromi herself. I don’t know.
Closure as a psychological notion from the Gestalts is largely about “image constancy,” which means that you can have a single image with pieces missing and still understand the whole. In daily perception, we experience this anytime one object covers up parts of another one. Despite that part is covered up, we still understand that there is a whole object beneath it.1
Using closure to address the parts of a character is much different because they all exist simultaneously. Moreover, I’m using it in a rather reversed way: we view the characters as a whole in terms of levels of depth (visual, personality, ideology) – ie. we “flatten” the image – yet cannot realize that many characters are constructed through highly repetitive signifying practices that link these three disparate pieces and make them seem naturally, inextricably bound to one another when, in reality, there isn’t such a thing as causality and indexicality between appearance, personality and ideology and values. It doesn’t exist, it’s discursive. We, as viewers and consumers, have been inculcated in the logic that appearance somehow points to a “corresponding” ideology when the truth is that these things have no relation to one another, they exist autonomously and it’s the huge reserve of representational power that anime and media holds which is able to make such statements without us, for the most part, realizing it.
 Not the words of McCloud, but his brief definition “the phenomenon of observing the parts but perceiving the whole” needed slight elucidation.