Jarco was the romantic pairing between Marco and Jackie.
The beginning of the ship's history is the episode "Matchmaker", where Marco is noticed by Star to be love-struck when seeing Jackie come by. When the class is celebrating Star for getting Ms. Skullnick to leave, she tells them it was Marco's own doing, in order to impress Jackie. While this works for a second, Jackie even praising him, it ends in embarrassment when Ms. Skullnick comes back and hands out a pop quiz, causing Jackie to walk away. Despite this, Marco excitedly tells Star that's "The most she's ever talked to [him]."
Jackie's next interaction with Marco is in "Monster Arm", where she (along with Hope and Janna) clamor around Marco's magically mutated arm.
In "Cheer Up Star", Marco, during his bad day, accidentally ends up breaking Jackie's skateboard, a fact she tries to play off nonchalantly.
During "Brittany's Party", Marco attempts to impress Jackie but is halted by his bout of car sickness.
In "Freeze Day", it is revealed that Marco has had a crush on Jackie since at least kindergarten, while all he's done during that time is share a nod with her every day. At the end of the episode, Marco says hi to Jackie for the first time in his life.
In "Interdimensional Field Trip", Marco is revealed to have been using his phone to send cute cat memes in an attempt to impress her.
Despite being on a field trip, that of one in a completely new dimension, Marco spends all of his time on his phone trying to impress her. After being captured with the rest of the class by the Universe's Most Dangerous Creature, Jackie texts Marco pleading for help. When Marco arrives along with Star and Ms. Skullnick, she exclaims his name in joy. Marco, however, becomes to nervous to help her up, much to Jackie's confusion, and she is eventually helped out by Star. At the end of the episode, Jackie asks if she can sit next to him on the bus, to which Marco(after getting the "thumbs up" from Star) agrees to.
Later, in "Marco Grows A Beard", Jackie greets Marco, then compliments Blake's beard, much to Marco's dismay.
In "Girls Day Out", Jackie appears behind Marco after getting his arm stuck in a pipe, asking if he needs help, which he attempts to play off.
In "Sleepover", Marco tries to impress Jackie with smooth jazz, a blue vest, and sunglasses. They are eventually drawn into playing a game of "Truth or Punishment", one that Marco at first tries to avoid playing, but is convinced to do so by Star. After being asked about their favorite color and thoughts on Star's brownies, they are asked a final question of "Who do you have a crush on?". Jackie reveals that her crush is on a boy she met at a skateboard camp the previous summer, and Marco finally reveals his crush on her, to Jackie's surprise. The game recognized that someone has lied about their crush (later revealed to be Star), and Marco, being pressured by the others whether he lied, makes a speech about
how he doesn't know whether he likes Jackie, or just the image of her, but that she deserves someone who wants to "get to know her", which he clarifies as himself. The game reveals then that he wasn't the one who lied, and Star berates it for being cruel to them, saying that lying isn't "black and white", and how opinions can change in the spur of the moment. To give an example, Star asks Jackie who she has a crush on, with Jackie replying "I don't know anymore". After defeating the game and throwing it into the trash, the group leaves, with Marco saying goodbye to Jackie and Jackie telling him that she'll see him at school.
In "Bon Bon the Birthday Clown", Jackie asks Marco out to their school's dance. Later in the episode, Jackie asks if Marco instead wants to go on a date with her in which Marco says yes to. In the same episode, Jackie and Marco share a kiss, which is interrupted by the blood moon.
In "Raid the Cave", Marco, in the beginning of the episode, is on a phone call with Jackie.
In "Just Friends", Star invites Jackie to a Love Sentence concert with her and Marco, and Jackie happily joins. Jackie and Star get along very well throughout the episode, Jackie even made Marco a skateboard to ride. But Marco ends up feeling left out as he watches Jackie and Star getting along with each other and tells them to go on along without him. Jackie helps cheer him up however, and the three proceed to go to the concert together. Marco and
Jackie start dancing together and end up kissing at the concert, making things a little bit awkward for Star. Jackie officially becomes Marco's girlfriend after the events of the concert.
Jackie returns in "Starcrushed", and as Marco is feeling uncomfortable after the events of "Face The Music", she understandably goes and helps cheer him up, being a very supportive girlfriend. They get along very well in the episode and play a game where they try to read each other's minds, and feed each other pizza nuggets. Both are understandably surprised when Star reveals her crush at the end of
the episode, but their opinions on the matter have yet to be focused on in an episode.
In "Rest in Pudding" we briefly see Marco and Jackie having lunch together, along with Janna. This is the first time Jackie is seen after the Season 2 Finale.
In "Sophomore Slump" Jackie and Marco go on a "the ultimate date", but Marco can't stop thinking about Mewni.
Jackie realizes their relationship will fall apart because of this and she decides to break up with Marco to let him go to Mewni. Marco is dissembled by this, claiming Jackie is his 'best friend', but Jackie smiles sadly and rightfully says they both know that isn't true, and skateboards away after telling Marco to 'stay amazing'. Marco moves to Mewni afterwards.
In "Britta's Tacos," Marco becomes worried about how Jackie feels about him after their breakup. Fortunately, Jackie has no harsh feelings towards him, and simply says that" They weren't the right match."
Popularity in the Fandom
Jarco/Mackie, despite having canon reasoning behind it since its conception, has always been one of the smaller pairings shipped in the fandom. This is partly due to the overwhelming majority of fans shipping Starco instead. Despite this, there is still an good amount of support for the ship. The ship has seen a slight boost in popularity ever since Marco revealed his crush to Jackie in "Sleepover", but has never reached the popularity of Starco or other ships.
This ship, however, gets a lot of unnecessary hate from the fandom. Although the fandom can be aggressively rude towards other pairings, this ship gets the worst out of all of it and hates towards it is much more vocal and easy to find. The fandom regularly depicts and predicts the two breaking up, usually at Star's expense, or even demonizing both Jackie and Marco for Star being upset. It's usually the treatment of this ship, and of Jackie and Marco, that especially gives the Starco fandom a bit of a bad name. Although it should also be noted that this major hate between ships really got intense around the time of "Bon Bon the Birthday Clown" where after witnessing the episode, a large amour of "Starco is dead" posts and fan art was circulated by various Jarco shippers included were offensive scenes, such as Jackie drinking a mug of Star's tears or Marco and Jackie making out in front of or on top of a heartbroken Star, this seemed to be the point in which the shipping war turned extremely aggressive towards each other.
There is not always a lot of support for this relationship, but there are plenty of people out there who really do enjoy it and make content for it. Jackie has warmed up to a good portion of the fandom as of lately. Her absence in the new intro did worry some fans but the crew has assured she has a role in Season 3 and she's not going anywhere anytime soon.
After their infamous breakup, many people were sad to see them go and wished they'd stayed together a little longer. This feeling wasn't limited to just Jarco shippers.
In “Britta‘s Tacos“ Jackie was finally seen again and was shown to not hold any grudges against Marco.