Chainsaw Man vs JoJo's Bizarre Adventure

Connection:

Both are the leaders of factions (the Devil Hunters and The Locacaca Organization) that contain members of people with special abilities that use spirits as their main attacks (Devils and Stands respectively)

Both have high ranking positions in an organization focused on public safety (Makima being head of the Public Devil Hunter Bureau and the Tooru (or at least WoU) being the head doctor of the TG University Hospital)

Both, at times, carry heavy apathetic attitudes towards normal people, Devils, and Rock Humans alike, seeming to have no care for who they hurt and the actions they commit to reach their end goals

Both are antagonists to a protagonist who is a fusion of two beings (Denji and Puchita, and Josefumi and Kira)

These two pretend to be extremely caring individuals that are tied to the main characters in some way (Makima taking in Denji and Tooru having dated Josuke's love interest Yasuho) until they reveal that they are in fact cold and manipulative people that share no affection towards anyone or anything but themselves and their image

They both treat other people like or have a very large and a bit odd interest in a certain animal (Makima's dog thing and Tooru with wasps)

Both a variety of lesser beings, to them and in their species', as pawns so that they have to do less work or get their hands dirty, having full control over them (Makima with the multitude of Devils and Devil Hunters at her disposal, and Tooru and Wonder of U with the Rock Insects and the other members of the Locacaca Organization)

Both want to attain the thing that allowed are protagonists to fuse (the heart of Pochita and the new Lokakaka)

Both ruthlessly murdered characters both of the main characters of Chainsaw Man and JoJolion considered best friends right in front of their eyes (Power and Rai Mamezuku). The two also being the murderers of two people both Denji and Josuke highly considered to be family (Once again, Power for Denji, and Jobin Higashikata for Josuke)

The two are also responsible for near millions of deaths in Japan alone with just their influence (Makima having to be responsible for effectively all the Devil Hunters that she has gotten killed, the Fiends, regular people, and all the Devils her people have killed. Meanwhile, Tooru is very likely, and highly implied, to be the reason Japan had entered World War II when they did. The reason being, calamity was preventing Lucy Steel and Joseph Joester from entering Japan again in order to pursue Tooru and the Locacaca.)

Both faked their love with a main character (Denji and Yasuho), effectively grooming them over time to love them, to trust them most, only to reveal they were the true antagonists and that they, in fact, never cared about them at all

Both appeared throughout the lives of our main protagonists (Makima was fighting the Chainsaw Devil before it transformed into Pochita and was taken in by Denji while Tooru appeared several times throughout Yasuho's life and was responsible for killing Rai's parents). After their facades are uncovered and they reveal their true natures, they both also reveal that they themselves are part of the creatures that the main characters have been fighting this whole time. In fact, they are practically their leaders (Makima turning out to be a Devil and Tooru revealing himself as a Rock Human)

Both, after their reveal, turn out to have one of the strongest abilities in their respective series' and universe which actually embodies something, behind the guise of the character they wanted people to believe they were (Makima being the Control Devil which embodies the fear of control or conquest, and Tooru being the Stand User of Wonder of U which embodies the Flow of Calamity).

Both meet an untimely and unfortunate demise at the hands of the protagonist using very specific abilities that were capable of bypassing these two's own ability to stay alive, despite practically all odds saying otherwise (Makima was defeated after Denji killed her not out of hatred but out of love, and Tooru was hit from an attack where the intent wasn't to attack him, but to save someone else), and would have to be put down for good by an attack relating to existence erasure (Denji eating Makima, with Denji being the hybrid of the Chainsaw Devil who erases what he eats, and Gappy using Soft and Wet: Go Beyond to erase Wonder of U).