Once something gets popular, there’s always a bandwagon that forms to make the most of its momentum until it comes to a stop. It happens to everything, including anime. Art styles change, stories get refined, and shows fall in and out of favor as tastes evolve.
Luckily for some shows and genres, they get to stick around even once their peak has passed. Mecha fans will always find something to scratch their robot itch. The formula for battle shonen anime hasn’t really changed that much since Dragon Ball and Yu Yu Hakusho. But other trends weren't so lucky.
7 Sukeban Anime
The older and younger generations will always clash with each other. It's why humanity has seen cultural shifts in nearly every medium, be it rock n' roll in the 1950s, or different forms of avant-garde art. 1980s Japan saw the rise of shows and comics about juvenile delinquents, with 'sukeban'- punk schoolgirls- catching on in particular as they either caused trouble or shut it down.
For example, Sukeban Deka, a manga about a punk girl working undercover for the police, was so popular it inspired two OVAs, three live-action movies, and multiple TV dramas. Hana no Asuka-gumi, which followed a gang of sukeban fighting other punks, also received 2 OVAs and similar acclaim. As did Tales of Yajikita College and the more comedic Project A-ko. The trend faded out by the 1990s, but leads with attitude would only get more popular in the following decade.
6 Edgy Dubs, Edgier Content
One of the reasons anime caught on as its own thing was its more mature focus. The likes of Akira and Ghost in the Shell were more adult and in-depth to fit alongside Disney classics on store shelves. Their tone was why distributors like Manga Entertainment went all-in on bringing over as many 'grown-up' movies, series and OVAs as they could. The 1990s saw the rise of edgy content, and some of these early entries were the edgiest of all.
For every cult classic like Wicked City and Ninja Scroll, there were terrible over-the-top examples like the gross Apocalypse Zero, the nihilistic Violence Jack, and terrible Angel Cop. If dubs could translate an insult into a curse, they'd go for it and double down. While blood, boobs, and bad language will always have their appeal, they're generally more refined today thanks to newer forms of distribution and evolving tastes.
5 Pokeclones
Those series got away with it because they were usually released direct-to-video or shown very late at night away from young eyes. Good 90s kids who stuck to their programming would get gentler affairs. The biggest of which was Pokemon. The tie-in to the Nintendo games was a force to be reckoned with during the tail end of the decade and start of the 21st century.
So, other studios got in on the action. Digimontweaked the formula by making their equivalents virtual pets, while Monster Rancher used an isekai fantasy setting. That’s without getting into Bakugan Battle Brawlers, Legendz, Fighting Food-ons, etc. They’re less common nowadays, with Yo-Kai Watch perhaps being the most notable Pokeclone running today. The rest either stuck to games or disappeared entirely.
4 The Evangelion Bandwagon
Neon Genesis Evangelion didn’t destroy the mecha genre, though it still stood out from the pack. It was more introspective than Mobile Suit Gundam, more tense than Macross, and had a dark tone of its own. The series was almost its own thing entirely compared to the rest of the genre. Nonetheless, other series would use it as inspiration to provide something much more moody, albeit not as blatantly as the Pokeclones.
The mech vs alien show RahXephon started off more directly taking EVA traits (e.g. the intro) before gradually mixing in its own elements. Likewise, Sōkyū no Fafner also used EVA-like tropes with its pilot & mech mental connections without outright hitting the same beats. The same couldn't be said for De:vadasy, which copied EVA’s character archetypes and plot turns nearly word for word while throwing in a gross adult turn that left it as a bad memory for those who saw it.
3 A Harem of Harems
The start of the harem genre, where the lead is surrounded by suitors that leave them conflicted, is generally credited to manga maestro Rumiko Takahashi and her 1980s breakout hit Urusei Yatsura. But the genre hit its peak in the 1990s and 2000s with shows like Tenchi Muyo, Ranma ½, Love Hina, and Ouran High School Host Club catching on with fans after some wish fulfillment.
The genre hasn’t disappeared since its arrival, as the formula of pretty babes/hunks is always a crowd pleaser. It's just not as dense or as shameless as it once was. Modern successes like KonoSuba and My Next Life as a Villainess mix in a hefty dose of self-referential irony to make the eye candy more palatable, alongside newer trends like isekai and light novel female antagonists.
2 Slapstick Abuse
Slapstick violence has been a flagship of animation since its beginning. However, there's a kind of uncanny valley to on-screen fights. The term is usually used to describe the icky feeling people get from characters who are too unrealistic to be human, yet too realistic to be fantasy figures (see Renesmee in the Twilight films). With violence, if it’s too cartoony to be an action stunt fest or horror scene, but too raw to be a wacky gag, it can just feel off.
Shows like Ken Akamatsu's Love Hina are good examples of this lack of balance. Keitaro being smacked around by his suitors was meant to be more slapstick. However, in context it can feel more like abuse today. Modern anime tends to balance the two out more evenly by either toning it down to something more appropriate or going all Looney Toons with it (Nichijō’s Misato, the 'Gundere', breaks out literal firearms around her crush, but never hits anything).
1 The Glomp
At least that sort of thing stayed in anime, right? The fans didn’t start copying those gestures because they thought it’d be cute…did they? True, they weren’t uppercutting each other to the moon a la Love Hina. They did glomp each other though. It was a running tackle that overly enthusiastic characters did towards their friends and loved ones like in Ranma ½ and similar shows.
Fans would replicate it with groups or at conventions, which became such a problem that many cons banned it to protect cosplayers and guest stars from getting hurt. It would join other fandom foibles like the infamous yaoi paddles in notoriety before largely disappearing from the community at large. Which is for the best.