Kyle can't figure out why Ike and his friends want to watch people comment on things going on around them rather than experience it for themselves. Meanwhile, the Marsh family needs money after Stan spent it all on freemium games so, Randy is forced to perform live to bring in some cash.
Kyle rushes home to play video games and bond with his brother Ike. However, Ike is not interested, as he is instead watching a video of Internet celebrity PewDiePie playing the game and offering commentary online, a practice known as Let's Play
(LP). Kyle is perplexed that Ike and other children seem to be entertained more by rehashed content. Despite his dismissal of LP, Cartman soon takes up the hobby himself, offering commentary on videos he recorded of Kyle and Stan, which infuriates Kyle, in particular because among Cartman's subscribers is Ike.
Meanwhile, Randy Marsh learns of an upcoming local benefit concert that will feature a roster of top pop musicians, including his female stage persona, Lorde. Randy calls his producer to refuse to play the concert, due to his reliance on pitch correction software, but the producer reminds Randy that he needs the money due to his son Stan's spending on freemium gaming. Reluctantly, Randy decides to appear at the concert when his daughter Shelly, expresses a desire to see her idol, Lorde in concert, because, as Shelly explains, Lorde is "real".
Backstage at the concert, Randy again hesitates to go on stage, but his producer tells him that the audience does not care what singers sound like, telling Randy, "Just go out there and pump your hips and rub your clit." When Randy says that that is not what his music is about, Iggy Azalea perceives this as self-importance on Randy's part, and gets into a brief altercation with him. Later, when Azalea performs with a hologram of Michael Jackson, Randy feels like something is being "lost" by rehashing dead celebrities.
Kyle invites Ike's friends over to his house to play video games, but all of them are watching various video game commentary channels on their mobile devices in Ike's bedroom. When told that video games should be played in the living room, the children dimiss Kyle and Stan as out-of-touch "grandpas", while Stan is convinced that his own generation is superior to theirs, and Kyle perceives his living room to be "dying".
When Randy's performance begins, his off-key singing and poor live performance turn the fans against him. He accidentally sets the Michael Jackson hologram free, and then rubs his groin in an attempt to win the audience back, but this only makes them angrier and leads to a disillusioned Shelly tearing her Lorde poster off her bedroom wall. When Randy calls his producer, his producer says that pop star fame has never been about music, but the publicity generated by performers' antics, which Randy has now generated. Randy resolves to reveal his identity publicly.
Meanwhile, the Jackson hologram is seen on a bus heading toward South Park, because as he explains, he needs to "take care of some important business". In response to his escape, the company that created him, Syntech Hologram Company, activates their hologram of Tupac Shakur Hologram, who steals a car and goes out in pursuit of Jackson.
Randy meets with his producer to tell him that he will reveal publicly that he is Lorde. The producer responds that artists are merely exploited to generate revenue, and that a hologram of Lorde will appear on The Tonight Show Starring Jimmy Fallon, and will expose her anus to create more publicity. Seeing Randy as an obstacle to this plan, the producer's henchmen attempt to restrain Randy, but Randy escapes to his home. When he tells his wife, Sharon this, she is incredulous that she just slept with a hologram, though the hologram turns out to be Shakur's, and not Randy's.
Randy's producer conspires with Cartman to install Cartman as the leader in an upcoming social revolution involving holograms.
AV Club gave "#REHASH" a "B+" rating saying: "That all snaps into place at the end, when it becomes clear that “#Rehash” isn’t really a spread-thin topical parody (or at least not primarily one). It’s the first part of a two-part episode, and in that light a lot of the flaws start to make sense. Two-parters are notoriously difficult to pace, because they almost never really have enough story for two episodes, instead choosing to split off with a cliffhanger somewhere to garner more eyeballs for the conclusion. So the first half usually lags, which is what’s happening here. South Park has pulled off successful"
IGN gave "#REHASH" a "7.8" rating saying: "This week's South Park was a culmination of several storylines in Season 18, most notably Randy's music career. It also introduced a solid storyline for Kyle, whose fear of losing the living room experience was relatable and even somber at times. Cartman's new online persona played well into this too and helped broaden the episode's scope. However, "#Rehash" went a little overboard with additional references and subplots (particularly the hologram/Terminator one). Hopefully these will be continued and concluded in next week's finale, but on its own, this episode didn't feel altogether there."