[4Tran]

Originally Posted by 0utf0xZer0

So it occurs to me that little sisters characters are usually either the protagonist's sister, the little sister of a more prominent female character, or not really a little sister at all, but merely a character who exhibits traits typical for a little sister character.

Why is it that's it's so rare for little sisters to have an older brother who is not the protagonist? Seems like they'd have some serious comedic potential, particularly if the older brother is a friend of the protagonist, yet I can only think of a few examples with Mei from Clannad being perhaps the most prominent.

In most anime, siblings in the show are more likely to be related to the protagonist than not. The obvious reason is that stories tend to revolve around the protagonist so non-protagonist relationships aren't going to matter as much. Since this principle is as true in other kinds of stories, you'll see the same phenomenon in non-Japanese movies, books, and so on.

Similarly, in most anime, siblings are a relatively good distribution of older/younger brothers and sisters in the mix. There are some genre-related quirks though, and the general prevalence of protagonists with attached imouto probably stems from the fact that it's extremely common in bishoujo shows. Moreover, as other posters have pointed out, it's also very common for non-protagonist male characters to get the short shift in those same bishoujo shows. The reason seems to be pretty obvious - the characteristics of female characters in these shows tend to be built around two aspects: charm points and story hooks. Being a younger sister of either the protagonist or his love interest fulfills both aspects while being the younger sister of the protagonist's male friend only provides a story hook. And since story hooks about a non-love interest usually run counter to the goals of a shounen romance, they aren't seen very often.

Another way to look at this topic is to tally up the number of character who seem to come from single-child families. There's no interest in dealing with their siblings, so they simply aren't given any.

Since most shows nowadays are bishoujo shows, any phenomenon associated with them will seem to apply to anime as a whole. Step away from bishoujo shows, and non-protagonist siblings are rare, but you'll see a few little sisters. I've only watched about a dozen shows this year, but I did see them in Aquarion EVOL and Moyashimon Returns.

As a side note, in Hollywood TV and film, you'll often see the protagonist have his friend's sister or his mentor's daughter as a love interest. This is just as much of a genre-quirk as the protagonist's imouto and they serve to satisfy similar goals. The main difference is that they are designed for different audiences.