Red Oni, Blue Oni/Video Games/Visual Novel


 * Twin sisters of the Nasuverse, Aoko and Touko, are this. One is chaotic, the other lawful. Touko was originally depicted as having blue hair until the Kara no Kyoukai: OAV gave her an Adaptation Dye Job to resemble her twin sister more. Genetics beats out symbolism these days. Nevertheless, their Mage Titles are "Red" and "Blue". (Don't bring it up, it's a sore subject.)
 * Archer and Lancer of Fate/stay night provide the first Servant duel in the game and are dressed in red and blue respectively. They are often shown battling each other in promotional materials as well as during the UBW intro (they also have a rematch late in UBW), invoking this sort of dynamic. Their colour schemes and personalities traits are reverse, however: Lancer is a hot-headed Blood Knight, while Archer is a cold and calculating Combat Pragmatist and Fallen Hero.
 * Played straight with Rin and Saber.
 * Mion of Higurashi no Naku Koro ni has a tattoo of a blue oni, prominently featured in the opening. However, she's far more like the red oni in terms of personality.
 * Also, in episode 20 of Higurashi no Naku Koro Ni Kai, says "If  is a flame that burns red, then  is a quiet, blue flame!"
 * Hot-Blooded fighter Kid and calm magician Magil in Radical Dreamers.