While most Digimon fans first encountered the series during childhood, the show features some surprisingly mature themes. A few reasons why Digimon wasn't for kids include the rampant string of death plaguing both Digimon and human characters, plotlines involving organ harvesting rings, and fish monsters wanting to mate with an 11-year-old girl.
That's simply scratching the surface - there are many more questionable moments in the series. For this reason, it's an anime worth a rewatch as an adult, though kids today should view it with caution.
Divermon (known as Scubamon in the dub) is a deep-sea monster who wants something decidedly not kid-friendly from Kari. A squadron of Divermon attempt to kidnap her, claiming they want her to bear their children so they can increase their numbers and overthrow their leader.
The creatures also talk about how pure Kari is, which is shockingly lascivious given the context. The dub eliminated the mating plotline for understandable reasons, but even without this, Kari still gets kidnapped by freaky fish monsters.
Jeri Katou's character arc incorporates several painful themes routinely cropping up in Digimon. First, her mother dies, which traumatizes her and makes it impossible to connect with her new stepmother. Later, her partner Digimon dies.
The resulting trauma from these compounded losses makes Jeri a prime target for the D-Reaper. He kidnaps and tries to brainwash her into believing humans deserve to die.
This leads to a shockingly occult nightmare wherein Jeri runs scared through the halls of a hospital, while shadowy figures pursue her and advocate the D-Reaper's macabre worldview.
The D-Reaper intends to destroy all life in the Digital World after the population exceeds a certain capacity. To make matters worse, the US government created the D-Reaper to keep the system from overloading.
This wouldn't be so bad if the Digital World were actually a computer program, but its residents are seemingly alive. Essentially, Digimon suggests the American government is 100% okay with genocide as long as valuable resources are at stake.
Yukio Oikawa's story is not particularly kid-friendly. As a child, he and his best friend Hiroki Hida grew obsessed with the Digital World and promised each other to one day make it there.
The two pals grow apart when Hiroki's father decides Yukio is a bad influence, but they still care about each other and hold the promise in their hearts. As an adult, Hiroki becomes a police officer and dies in the line of duty, compelling Yukio to venture to the Digital World.
Yukio's desperation - along with his possession by a Digimon vampire - leads him to commit atrocious acts. He creates Digimon who kidnap children, and manipulates Ken into becoming the evil Digimon emperor. When he eventually dies, the Digital World is within reach, but he never gets to visit it.