Skullgirls vs Chainsaw Man

Connection:

Both are young, white-wearing teen protagonists of popular anime-esque forms of media, who live in a world massively infested by various eldritch horrors that prey on humanity (Skullgirls, Parasites and Devils respectively)

Both are members of a race of beings primarily known for their unique bond with one of these supernatural beings (Filia is a Parasite user while Denji is a Devil Hybrid)

Both would at some point meet cute dogs that are actually one of these supernatural beings (Filia would meet a dog that acted as the host for the hair parasite Samson, Denji would meet Pochita, the Chainsaw Devil, at his father's grave)

Both had fathers who dealt with the mafia (Filia's dad is the son of the Medici mafia's leader, Denji's father had dealings and debts with the Yakuza). This connection to the mafia world later come to bite them in the ass after said mafia betrayed them due to their dealings with a supernatural being (Filia and her family would be betrayed and assassinated by the Medici after the mafia caught wind of their encounter with a Skullgirl. Meanwhile Denji would be betrayed and killed by the Yakuza after they were promised incredible power by the Zombie Devil). Luckily, in a near death state, they would be rescued by their supernatural canine partners, who would merge with their bodies and modify them, granting them the powers they use today after assimilating one of their body parts (Samson abandoned his dog's body and merged with Filia's hair, whereas Pochita merged with Denji's heart)

Coincidentally, both mergings have connections to their user's hearts/minds (Samson merging with Filia accidentally caused her to lose all her memories. Pochita merged with Denji due to his adoration of Denji's dreams and a want to see them fulfilled)

Both have the ability to weaponize their own bodies in some way, utilizing sharp blades to cut through their supernatural opposition (Samson weaponized Filia's hair, Denji can sprout chainsaws from his body)

Both would soon come in contact with an ancient acquaintance who is deeply infatuated with their supernatural partner (Eliza and Makima respectively), and become their slaves (Eliza defeated Filia and enslaved her and Samson against their will in Ezlia's story mode, whereas Makima made Denji her servant under the threat of killing him as a Devil should he refuse)

After a fight, both would make friends with a calmer, more sophisticated person, who uses a white supernatural partner to fight, and whom they would later see dying in front of them (Filia would meet and befriend Squigly, who fights alongside her Parasite Leviathan, and who died after the destruction of the Skullheart. Denji would befriend Aki, who fights alongside his Contract Devils which include the Fox Devil Kon, and who was later killed by Denji himself after becoming the Gun Fiend)

Both have an alternate transformation that occurs once their supernatural partner takes over their body and suppresses their human self (Samson can transform into a giant hair demon by taking over Filia's body, Pochita can enter his True Devil Form after Denji abandons his contract with him)

Both supernatural partners have a history of infamy (or fame) among their species due to their heroic deeds (Samson is one of the few Parasites who defied Sekhmet's conquest, whereas The Chainsaw Devil is known as the Hero of Hell after he saved millions of demons from a catastrophe in Hell)

Both would participate in a final clash against their greatest, most important enemy (Marie and Makima respectively), where they would soundly defeat them and absorb something from them (Filia would defeat Marie and wish on the Skullheart, becoming a Skullgirl later on, while Denji would defeat Makima and devoured her, permanently killing her for good)