Something I appreciate seeing in storytelling (mostly anime) is when the differences of two character’s methods are portrayed in such a way that neither method is always going to work. I find the idea of a character’s approach succeeding in one circumstance versus failing in another favorable over the idea of a character’s disposition being indomitably prosperous in the face of all forms of adversity to overstate an unrealistic message (e.g. a character stubbornly determined about being nice to everyone will triumph over all evil).
Whereas, it is vastly more satisfying seeing two characters, friends or rivals, be given multiple opportunities in a story to apply their own way of doing things and present both methods as advantageous in different and similar situations. Take a typical honest, kind and naive protagonist with a sincere smile and heart that can win over almost anyone with a morally good conscience, or a lacking in friends, and place him with someone who’s more conniving and devious, and immune to such charms. Extracting information might work for in the first scenario for him, but would most likely fail in the second. That’s where you add the more outspoken and intimidating character with a strong sense of mischief. While his approach may not work for the first scenario, it does have a much higher chance of success for the second.
Not to get too technical, but I just find it refreshing to see stories express contrasting temperaments and multiple walks of life as flavours, rather than ranking them in terms of acceptability in society, or highlighting one as the ideal pinnacle of excellence and decency. Whether a certain attitude is respectable or not should not dismiss the value of that type of mindset or behaviour in other areas, such as pragmatism, logistics, and creativity. Being kind and honest is an appreciable quality, especially if you use it in correspondence with themes of love, friendship and understanding. But, rejecting all other forms of thinking and means of solving problems is shortsighted and impractical.
And while I am fond of the foil and rival tropes that go together with a more overt form of contrast, there’s a more specific version of duality I have in mind. Nagisa Shiota and Karma Akabane from Assassination Classroom stick to mind as a fairly decent criterion for the type of duality I’m aiming for. Visually, the pair are already contrastive; blue hair against red hair. However, they both follow a similar path throughout the series and their goal for the most part is ultimately the same; assassinate Koro-sensei.
Of course, what separates the two as a pair from duos in most anime is that they are friends, not rivals, and the differences highlighted between them are specifically geared toward their methodology in assassination. But at the same time their individual approaches against adversaries and obstacles in varying conditions distinguishes them from each other in a very particular way, that does end eventually culminate with them at odds against one another (in a paintball match of all things).
Nagisa, on the surface is short, meek and androgynous. making him seem kind and harmless. Despite being a genuinely sweet kid who gets along with most of his classmates, Nagisa is well-versed in stealth and analysis of other’s weaknesses. His tactics are cold and calculating, and involve little hesitation. Compare that to Karma, who is more physically capable than Nagisa, has psychopathic tendencies, and is a combat pragmatist, where his true talent lies in his traps and intelligence.
I’m only scraping the surface in terms of their character, but the important thing to take away from this is that while they are similar in many aspects, they both lack something the other has. Karma is so arrogant and proud that he treats failure as a humiliation (until his character development), whereas Nagisa isn’t too proud to get down on his hands and knees and beg (to help his friends).
These qualities separate the characters’ strengths and weaknesses, and help us determine whose way of handling things is more suited for certain situations. And the presence they have on screen is dictated by their demeanor and juxtaposition to the other (hence, red oni, blue oni) At least, I think it’s a neat idea and one I’d like to see appear more often in not just anime, but other visual mediums and books as well.