Comic relief in the form of siblings who never stop fighting.
Do we have this already? Needs a better title... Siblings rivalry distilled into a running gag. Basically, two siblings (or more) whose only purpose in the story is to bicker or roughhouse. And not in an epic Cain and Abel way either. Simply put, the majority of their screen time together is spent with the two getting annoyed or angry with each other for utterly trivial reason. The humor being how utterly petty the two can be around each other. God help all if they have to share a room. The two tend to be secondary or minor characters in the story and are relatively common in children's shows. Almost always played for laughs. Note that not all "unpleasant" sibling relationships qualify. If it's just the older brother taking pleasure in tormenting the younger, then you have a Big Brother Bully. If the younger sibling is just a pest that the older sibling would rather ditch argue with, then you have an annoying younger sibling. If there is tension between the two but they prefer to express it by being distant (with the occasional bouts of violence) then you have an aloof big brother scenario. Also, siblings who've had a few arguments and snark at each other occasionally don't count. The key here is that arguing with each other is all they EVER do whenever they're in proximity of each other. The two have to be equally as petty and argumentative towards each other the majority of the time. This is why these characters tend to be minor characters, if they were given constant attention they'd get irritating really quickly. This trope is far more common in Western media then in Eastern; probably because most Asian cultures view elder siblings more as additional parents to the younger (if not outright parental substitutes) rather then equals to their younger sibling. This trope's lack of presence in anime is likely due to Japan's declining birth rate; both the creators and their audience tend to be only children so their portrayal of sibling relationships lean more towards ideal and rule of cute (when they're not writing a Cain and Abel scenerio). See also Hypocritical Heartwarming and My Sister is Off Limits for moments when the two will occasionally stop fighting. Compare Different as Night and Day, Sibling Yin Yang and The Glorious War of Sisterly Rivalry. The line "this is my side" is very common between these two. Contrast with Big Brother Complex, Blood Brothers, and Brother Sister Incest.