Half Arc Season

Sometimes, the writers of the show want the ability to tell a longer story that a Story Arc provides, but also want the flexibility that a more episodic structure gives. The answer to these is the Half Arc Season, a fairly new format that has picked up popularity as network syndication becomes less important.

Each season has its own Arc; however, the majority of the episodes in the season are one-part standalone episodes. The Arc is mostly separated out to the first few episodes of the season (to set it up) and the last few (to resolve it), with a few that push forward the greater storyline while still telling their own story sprinkled about in the middle.

Note that seasons mostly devoted to a Story Arc can still have the occasional standalone in them; it's when the majority of episodes are non-Arc that this trope applies. Usually, this is midway in Season Fluidity.

Examples of Half Arc Season include:

Anime and Manga

Ghost in the Shell: Stand Alone Complex; in this case, the Title Card of each episode would be marked 'Stand Alone' or 'Complex' (Arc-based). The second season went even further, with two arcs running simultaneously - "Individual" episodes tie into the first arc, "Dual" episodes with the second, and "Dividual" episodes were stand-alone.
Despite really only having one Story Arc, Cowboy Bebop still fits this trope.
Black Lagoon's layout contained 2-3 episode mini-arcs within both seasons (the Nazi arc, the Roberta arc, and the Triads and Terrorists arc from Season 1, as well as the Vampire Twins and Greenback Jane arcs from Season 2). Season 2, however, also featured the six-episode endgame "Fujiyama Gangster Paradise" which took up the other half of the whole series.
- And if the length of the "El Baile De La Muerte" arc from the manga is any consideration, we may be in for another long haul when Season 3 is animated.
  - We aren't, or, better, we are but in different way: it's being animated as an OVA.

Live-Action TV

Some seasons of Stargate SG-1, especially the last four.
Veronica Mars, two ways. Its first two seasons, though technically full arc seasons, had a lot of Mystery Of The Week with little or no movement on the season-arc story. Its third season had two distinct shorter arcs, one six episodes long, with beginning, middle, and end; and the second nine episodes long. The last five episodes of the season are standalone (excepting the last two episodes, which were aired together).
- The advantage, in a show like VM, is that some of the Mysteries of the Week can actually be key revelations in the arc, but this fact is not obvious until the end of the episode.
The new Battlestar Galactica did this though they leaned more towards every episode being part of the arc. The Season finale/premiers and the mid-season two-parters usually had some kind of game-changing event and the episodes after that were mostly stand-alone, exploring the results of those events and their effects on the characters while only prodding the story along.
The newer seasons of Doctor Who are leaning more and more towards this format as time progresses:
- In series 1, time and time again Rose and the Ninth Doctor encounter the words "Bad Wolf", but have no idea what they could be referring to. An episode midway through the season then sets the stage for the two-episode season finale where the reason behind the appearance of the Bad Wolf phrase is revealed.
- In series 2, a majority of the episodes are standalone, though again midway through there are two episodes which set up and foreshadow the events of the season finale.
- Done beautifully in series 4, where all of the episodes seem very episodic, with seemingly unconnected references. And then the finale comes, and suddenly nearly every episode was part of the story arc.
  - Series 3 was arguably a better example of this. Rather than Arc Words or "seemingly unconnected references", almost every episode slyly introduced a Chekhov's Gun that would be fired in the three-part finale: the Timey-Wimey Ball in "Smith and Jones" and "Blink", the chameleon arch in "Human Nature", Dr. Lazarus' experiments in... well, "The Lazarus Experiment", Mr. Saxon and the government keeping tabs on Martha in "The Lazarus Experiment" and "42", the Face of Boe's message in "Gridlock", and the power of words in "The Shakespeare Code".
- Let's also not forget series five and six, in which starting with the first episode of season five, silence is mentioned. The Doctor and Amy run forth on their adventures not giving a damn about the mention of silence or anything else. Several times throughout the series we hear about the silence, but our focus is drawn more towards the mother fucking CRACKS IN TIME. Enter series six which features a religious order opposed to the Doctor called the--(surprise surprise) Silence! And we can't forget the wonderful question that cannot be answered: Doctor Who?
Buffy the Vampire Slayer and Angel, Buffy in particular.
The last two seasons of Star Trek: Deep Space Nine, as well as the third season of Star Trek: Enterprise.
- A couple of Deep Space Nine episodes in the sixth and seventh seasons played with this trope: it appeared at first that they were standalone episodes not part of the Dominion War arc, but then the Dominion would show up unexpectedly and it would turn out to be part of the arc after all. A good example is "One Little Ship".
Season Two of Blakes Seven has a story arc that is mentioned in passing during the third episode and kicks off with the fifth and sixth episodes before getting partially sidelined until it becomes the center of attention in the last three episodes.
Burn Notice. Generally, a standalone mission takes up most of the screen time while the burn-related investigation gets only a few scenes scattered throughout the episode. Arguably, most episodes move the arc along a little, but it moves so slowly you could probably miss a couple episodes and still figure it out pretty easily.
- You can. Especially since most of it ends up being dead ends and the important bits are always repeated anyway.
Supernatural follows this pattern.
Smallville does things this way.
In the third season of Bones, this tactic was employed. The Gormogon arc was often made of awesome, but if you know how it ends it can be deeply unsatisfying, as the arc was cut short by the writer's strike and ended with an Ass Pull of epic proportions.
Leverage attempted this with its third season, but due to availability, odd timing, lack of scripts, etc. there was only one truly arc important episode between the premier and the finale, with some small hints thrown in here and there. Word of God states that these were meant to be spread out more, but shooting schedules clustered them into the back third of the season.
Tokusatsu shows go with this if they're meant to last a season. The Monster of the Week will still be sent by the Big Bad but otherwise unrelated and the overarching plot will be touched on in the beginning, the end and a few episodes in between. This carries over to Power Rangers as well.
Fringe generally has arc episodes at the beginning of the season, around the half way point (episode 10 and 11), during sweeps (15 and 16) and ending with a big finale. The rest of the episodes are "Freak of the Week" deals.
Chuck does this. Though the show does try to add plot points for the major arc in every episode, some of them are mostly self-contained.
X-Files was particularly famous for this, and the fandom still rages over whether it was better with the arc or without the arc and debates over what episodes count as arc related (generally, arc related episodes featured characters like The Lone Gunmen, Th Cigarette Smoking Man, Deep Throat, and Mr. X, and Alex Krychec) but several one-shot episodes featured them as well. The most debated is "Musings of a Cigarette Smoking Man" which was entirely based on the alien arc and showed a scene that was said to have happened before the series started, but added nothing to plot otherwise, and is even hinted at being false at some points.
While most Glee episodes are fairly stand-alone, there is the larger arc about the group preparing for competitions (Sectionals, Regionals, Nationals) which strings each season together.
Castle

Video Games

Even video games, which are released as a single work, seem to experience this, particularly RPGs. Square Enix's Kingdom Hearts II, for example, have almost half the Disney-based worlds with nothing at all to do with the more Final Fantasy-esque overarching storyline, and a few with only token appearances of the Quirky Miniboss Squad (save for Beast's Castle, which one of them only shows up in.)

Western Animation

Each season of Teen Titans except for the entirely arc-based fifth season, where a flashback origin story episode was the only one not related to the current world-travelling plot at hand.
Jackie Chan Adventures. Season 2 especially is notorious with this. The stand-alone episodes put together were longer than any of the other seasons.
- It should be mentioned that, with the exception of the first two seasons (which had the same Big Bad but different plot), all Big Bad villains for every season got their debut in a stand-alone, Tarakudo being the most triumphant as he was just a tattoo in the initial appearance.
Transformers Animated follows this format to an extent, particularly in the first season. Season 2 has some random, AllSpark-related hijinks between important episodes, but they were usually still related to the plot in some way, with the Blue Racer being a prime example.
- The first season of Beast Wars was similar, with various questions springing up (Tarantulas trying to get a stasis pod, the strange rock formation) to be left unanswered until the end. However, season 2 onwards had a much more serialized plot.
The first season of The Secret Saturdays did this.
Spider-Man: The Animated Series in its second, third, and fourth seasons. All of them had their own subtitle with the actual episode titles treated as chapters of it, but all had their share of standalone stories as well.
The first season of WITCH has the heroes going through a main standalone plot for each episode combined with scenes of the villains that advance the Myth Arc. The second season was a much more ongoing plot each episode.
Ben 10 was like this, with the majority of the episodes being standalone but a handful advancing either the seasonal arc or the overall Myth Arc about the Omnitrix.
Avatar did this in its first and third seasons. Season 2 had only a few self-contained episodes, and they were more important for tying up loose threads left over from the previous season.
Season One of My Little Pony Friendship Is Magic has an arc following the main 6 preparing for the Grand Galloping Gala in Canterlot, but every episode was also able to stand alone, including the arc episodes.