Love/Domination
I think that fundamentally Chainsaw Man is trying to explore the complex and inescapable power dynamics of social life, on both a macro and micro level. Starting with the family and expanding outwards to sex, work, and nationalism we can see how love, connection and identitydo not and cannot exist in a vacuum. Our relationships are not just complicated but the forces of dominaiton and oppression, in some ways they are our relatinpships. The two are inextricable.
I think the importance of food in the story supports this. Food is vital, as is love. But eating is always an exertion of power of something or someone else, even if that thing is just the food itself. And with all the cannibalism, it's pretty easy to see how the simultaneous intimacy and domination of eating something can be translated into human relationships.
The family is the most fundamental human relationship. I think it's pretty well known that the reason our main character is a chainsaw is because of the chainsaw's historical use in childbirth - the mother-child relationship is the central driving force of this series. The mother and child in part 1 are of course Makima and Denji. It's obvious from the beginning that Makima is using and abusing Denji. It's revealed towards the end of part 1 that Denji's father was violently abusive as well. Denji killed his father, and he goes on to kill his "mother" as well. He cuts Makima in two with a chainsaw - a fate already predicted by her name: ma-ki-ma, a mother split in half. She is reincarnated as Nayuta, who Denji tries to have a more equal relationship with. This is Denji's power- he kills the old forms of power and births new kinds of relationships.
Denji's relatinoship with Aki and Power is, while not totally horizontal, clearly founded in genuine love. But their relationships are not their own. Their little family was put together by Makima, and they can never have a life together. I think what's happening here is an exploration of how within a system of domination, even the most well-intentioned and loving people cannot abandon the world they live in and must capitulate to the demands of society. You can't ever really escape the inequality that's built into the world.
Makima is also our main characters' boss. And even though they're union (woo), their union rights seem to be in name only. I mean I guess they presumably used their PTO to go to Hokkaido, but what they can or can't do is ultimately up to Makima and they obviously have no real power in the workplace.
Every single sexual relationship in this series is insane. Denji literally cannot, will not stop getting molested and harrassed. Notably abused by Makima, obviously, who intentionally turns his mind towards sex as a way to control him. Molested also by Himeno. It's interesting that this is identified as a pattern of behaviour for her, that many of them have been kissed by a drunken Himeno. And that they all still love her afterwards. What she did to Denji was clearly wrong and they both acknowledge it, but Denji and Himeno go on to be friends and her death is a tragedy. This was a tough one for me to wrap my head around because I was so disgusted by her actions. But I think the entrenched nature of sexual harrassment and assault is kind of the point. In an organization run by Makima, the number one child abuser and award-winning sex offender, sexual exploitation is rampant and normalized. None of them really think anything of Himeno's misconduct because they are all experiencing and/or enacting similar kinds of degredation and mistreatment all of the time.
The sexual exploitation continues throughout the series. Reze, who is totally powerless in her situation, is forced by her government to pursue Denji sexually in order to kill him. The same thing is repeated in Part 2 with Asa, who is forced by Yoru to pursue Denji. Yoru even goes so far as to use Asa's body to have a sexual encounter with Denji, which is traumatizing for the both of them. Denji is also pursued by yet another adult woman in Part 2, Fumiko. Fumiko gives up her body metaphorically and literally for her job, which includes hitting on the teenager for reasons. I'm gonnabe honest I'll have to reread part 2 once it's done to fully grasp what was going with her. The point is that sexual relationships in the series are basically always exploitative and painful for one or both parties. People don't seem capable of entering into sexual relationships without some sort of external force altering their choices.
(Side note I looove that panel so much^. The panel splitting Asa's face as Yoru leaves, like it's showing you the split second Asa returns to herself and realizes what has happened. It's a good manga you guys.)
Belonging to any formal group means sacrificing your freedom, your body and your life. Being a citizen of a country means that that country can gamble with your life as it chooses, without your knowledge or consent. . See: Japan, the USA, the NRA, and to a certain extent, the USSR. Also wherever Santa Claus operates out of, is it England? or Germany? I don't remember. Anyways the point is the the family is a microcosm of society so the domination that occurs on the parent-child level is recreated at every level of society all the way to national citizenship. And yet we can't live without connection. Every time you kill the family, we'll just find a new one.