Detective Somerset: We must divorce ourselves from emotion here. No matter how hard it is, we have to remain focused on the details-This trope is about two individuals (or occasionally, factions or civilizations) that are significantly linked together somehow (such as through a rivalry, friendship, being siblings, co-workers, competitors, etc.) that have differing personalities and, with it, often different approaches to the world in general, especially whatever they might be competing in/for/over. This, of course, gives them something to butt heads about, since their manner of acting may rub each other the wrong way and each is sure that their way of doing things is right. By the way, don't get too stuck on the colors in the title. The title refers to a Japanese tradition that gets elaborated a bit later in the article, but it doesn't mean that a character has to dress in or be associated with a particular color in order to fit the role. Their personalities usually run roughly along the following lines: The Red Oni is associated with passion, wildness, and defiance. A red oni character is often more brawny than brainy, extroverted, enthusiastic, determined, and filled with a zest for life. He is also much more likely to break conventions and rules than his counterpart. Often an Idiot Hero or, in more mature pieces, a Boisterous Bruiser. If a red oni is indeed noticeably intelligent, he will still be much more emotional than the blue oni and/or with less sophisticated thoughts, feelings, or goals. When a villain, the red oni is often a Blood Knight. Generally speaking, they're more people-oriented than goal-oriented. They may or may not shrug off criticism about themselves or their aims and goals, but say or do something nasty to their closest friends and you've just guaranteed yourself a world of pain. Likely candidate for The McCoy. In terms of character alignment, the red oni tends towards the Chaotic alignments, though this isn't always the case. The Blue Oni is an opposite in most ways — more intellectual, proud, traditional, introverted, and cultured (sometimes more spiritual, although that's not guaranteed). Blue oni personalities are often respected by others, but also likely to puzzle or confound their peers because they are difficult to read and have a mysterious quality to them. Personality subtypes include The Stoic, The Spock, The Quiet One, and the ever popular Aloof Big Brother. It's worth noting that while blue types appear tremendously calm and composed, sometimes, this is just the surface, and scratching that facade may show that they are, if anything, wound far too tight beneath their calm and unemotional appearance. Villainous blue oni tend to be extremely ruthless, ready to do or sacrifice anything (and often anyone) to accomplish their goals. See Knight Templar and Well-Intentioned Extremist. Likely candidate for The Spock. In terms of character alignment, the blue oni tends towards the Lawful alignments though this isn't always the case. While many expressions of this trope play it straight, it is also not uncommon for the Blue Oni and Red Oni to subvert one another. The Red Oni, while usually the more passionate and emotion-driven, may also be the more easy-going and flexible of the two. His/her more simplistic world-view may make them at least partially immune to angst and Wangst. Conversely, the Blue Oni, while usually stoic and thoughtful, is often hiding a volatile, angsty nature that may erupt if pushed too far. In such instances the two may switch roles, with the Red Oni becoming the reassuring, composed partner and the Blue Oni becoming a Whirling Dervish of Rage! (Compare pairings such as Red Oni Ken (cocky, arrogant, but decidedly easy-going) and Blue Oni Ryu (stoic, disciplined, but brimming with internal conflict).) If Elemental Powers are present, you can usually expect the red oni to use Playing with Fire or something of a similarly flashy nature, while the blue oni will prefer Making a Splash or possibly be An Ice Person and an Elemental Rivalry is born. There are a lot of ways to play their interactions, so sometimes the two are both leads on an equal standing, sometimes the blue is more of The Smart Guy or The Lancer to the red's Hot Blooded lead. The relationship can also vary wildly, as they are just as likely to be close friends as they are to being bitter rivals or enemies. One thing that is sure is that regardless of how big a cast is, when these two are in it, they will be magnetically drawn to each other. Note that many times, this will be a relative, not an absolute, distinction: the Red Oni need not be The Fool and the Blue Oni need not be a Straw Vulcan. The name comes from traditional Japanese folklore where Oni (think troll/ogre) usually came in two flavors, a red and a blue. Over time, it's gotten popular to ascribe different qualities and personalities to the two colors. (Think the high-strung Type A personality and the easy-going Type B personality.) See also the Marid and Ifrits over at Our Genies Are Different. In a show where it's relevant, differences in fighting style may be something like Technician Versus Performer. For example, a red may rush headlong into combat without focus or a plan, while the blue may use cunning traps and strategies, or tend to win in elegant Single-Stroke Battle fashion, or rely on hitting a target with magical powers from a distance instead of running up to their opponent and punching them in the face. Force And Finesse is a variation where red tends to rely on raw power while blue uses precision strikes. Compare Outside Man, Inside Man, Odd Couple, Cast Calculus (for the evolution of the Red/Blue dynamic through various numbers of ensembles), Tomboy and Girly Girl, Sensitive Guy and Manly Man, and Order Versus Chaos. See also Pink Girl, Blue Boy, Action Duo. If the contrast in personalities between the two actually brings them to blows, you probably have a Tiger Versus Dragon situation. If they are friends it will often be of the Vitriolic Best Buds variety, most commonly Type 2.
Detective Mills: Hey man I feed off my emotions, ok? How's that? [Mills promptly gets into a fight with a reporter snooping around the crime scene] Hey man, I'm sorry. They just... they piss me off, ok?
Detective Somerset: It's ok. It's impressive to see a man feeding off his emotions.
All examples are listed in the red-then-blue order unless otherwise specified: