Chainsaw Man is a violent, crazy, gory, surreal manga about a man who becomes chainsaws to kill demons, as you do. Denji is one of society's lost people. Practically homeless, he earns his keep by hunting and killing devils with help from his cute chainsaw demon pet Pochita. When he's betrayed by his Yakuza boss, he merges with Pochita and gets revenge by going full chainsaw-crazy on them. This leads to his recruitment by Makina, the head of a government task force out to hunt devils. Thus begins his new career as a devil hunter with new friends and sidekicks, but things only get crazier.
Tatsuki Fujimoto has a flair for quiet poignance in his portrayal of sad Denji's life. He's alone, in debt (as many heroes in manga are these days to reflect a common dilemma many Japanese people live through), barely socialized, craving friends, romance, sex, and a sense of belonging in life. All this is offset by surreal, ridiculous and surreal violent and a unique sense of deadpan comic timing. It's the latter that makes the series unique.
Where other series might be deadly earnest, this one distinguishes itself with slapstick comedy. Deadly earnestness might have made it unreadable. Fujimoto seems to understand that, since his characters are sad, broken people who live outside the norms of society and haven't learned basic social skills.
Japanese manga has a hilariously and bizarrely literal relationship with titles. With a title like "Chainsaw Man," you would think this series was about a man with a chainsaw. Instead, we get a man who literally becomes Chainsaws, including his head. There seems to be a trend in manga right now of people who become anthropomorphized versions of deadly weapons and objects. No Guns Life features a private eye hero whose head is literally a giant gun.
The common subtext here is about people getting abused, degraded, dehumanized, objectified, literally becoming objects. Society is to blame for degrading people into tools and objects; these mangas seem to be saying, though they never outright blame Capitalism or the alienating repressiveness of Japanese society. The result is one of the more unique manga out there.