The crew from Shirobako view the fruits of their labor.
“Cour” refers to the airing period and is only applicable to TV series. One cour is one anime airing season and is three months long. Although the words are unrelated, it might be useful to think of it as the first syllable of “quarter” since it refers to one quarter of a year of air time. The title of 91 Days might refer to the 91 days a 13 episode series takes provided there aren’t any sports events or unforeseen circumstances to slow it down. Since a year is 52 episodes this means one quarter would be 13, but it’s common to go a few episodes under.
It’s understandable if it’s a bit confusing at first, as Black Rock Shooter, with 8 episodes and The Disappearance of Yuki Nagato, with 16 episodes, would both be considered one cour by most people even though one is twice as long as the other.
In the past, anime would take long rest periods without breaking the anime into separate seasons; although The Big O took the length of 14 cours to air it was only actually airing for two of those and should be looked at as a 2 cour anime.
Katanagatari is only 12 episodes, each being 50 minutes long, but it only released one episode every month so it is a 4 cour anime. Chi’s Sweet Home is 104 episodes long, each being 3 minutes long, and four episodes were released every week so it aired over six months making it a 2 cour anime. Princess Tutu had 14 episodes which were 24 minutes and 24 episodes which were 12 minutes. It aired over four seasons making it a 4 cour anime despite being the same length as a 2 cour anime.
Anime with short episodes such as Teekyuu are still the same amount of cours that they took to air. Kekkai Sensen was intended to be a one cour anime but the final episode was delayed well into the following season. Although it took two seasons to air it is still a one cour anime.
Kiss x Sis (OVA), Flag (ONA), and Magic Kaito (Special) all have 24 minute episodes and have 12 or 13 episodes like one cour anime do but, since they are not TV type anime and do not have regular airing schedules, they are not considered to have “cours.” Magic Kaito was aired on TV, but it was aired as a special series and was not aired at one episode per week.
Anime that are split into separate seasons are sometimes treated as more than one anime. A counterexample is Kirarin☆Revolution, a single anime that is 153 episodes long, which makes it 12 cour. On the other hand, Pretty Rhythm: Aurora Dream and its sequels Dear My Future and Rainbow Live are 51 episodes each adding up to 153 episodes… but they are three separate 4 cour anime.
With modern anime, producers have to choose an airing slot so going a bit over the cour limit (number of cours x 13 episodes) would be problematic. It’s safer to release a show as a one or two cour anime and then release the rest as OVAs or ONAs if they need more time. Gekisou! Rubenkaiser was fine airing its 17 episodes on TV over a ordinary air period back in 1977 while Kokoro Connect from 2012 had to use specials to air the last 4 episodes of its 17 episode run. Of course, this isn’t the only reason for airing anime like this, but older anime tended to stick to a single format when telling their stories.
Episode length can also be manipulated to tell the full story in the amount of episodes you have. Mirai Shounen Conan from Nippon Animation only has 26 episodes but, which episode lengths of 29 minutes each, it contains much more content than a typical 26 episode anime. Nippon Animation does a lot of interesting things with cours. They’ll make a number of 3 cour anime (30-43 episodes) and, since they adapt a lot of novels, it looks like they use the exact amount of time that it takes to properly adapt the novel. Back in the day, they aired one such adaptation a year, so they always took a full year to air them regardless of the anime’s length. This means that, by length, they ranged from 2 to 4 cour but they are all 4 cour anime.
It isn’t a common practice, but there are anime that air more than one episode a week. Massugu ni Ikou. aired 4 episodes over 4 days. Flowering Heart aired two half episodes a week, making it somewhat like a one cour anime despite having 26 episodes. ReLIFE takes this a step further when it aired all 13 of its episodes on the same day.
We might think of anime as always being a multiple of 12 or 13, but it’s just as important to know why they are as it is to know why they sometimes aren’t. Although anime fans do use the term “split-cour” to refer to an anime whose segments are split by one airing season, many will still use the word just to refer to the length so the air dates shouldn’t be what you look at when someone asks for anime under two cours.