A definite theme of dungeon meshi is that of selfishness and selflessness with pretty much every character defined by these two things in some way
most obviously there's the winged lion who's entire existence is defined by selfishness, he just consumes, consumes and consumes, ruining everybody, with labyrinth he is bound to and he himself encouraging and shaping the selfish and selfless desires of others. His greatest desire, to consume everybody is the ultimate act of selfishness in the series yet he frames it as and pretty genuinely views it as an act of great selflessness, which is part of another theme in the show of people imposing their selfless desires on to other people.
As can be seen with Marcille, from the beginning she is shown as the most outwardly selfless, she's the one always wanting to help other adventurers, aside from Laios the loudest advocate for rescuing Falin, resents Namari for abandoning Falin and is shocked to find out Chilchuck is doing this because he is being paid. She's the one who crosses all moral and ethical barriers to save Falin, to defeat the dungeon rabbits. And then we see how she has the greatest most all encompassing desire of them all, to equal everyone's lifespan to one thousand with a selfless motive behind it, that it will erase bigotry between races. The selflessness of it is something she is almost proud, she's insulted and very insistent that she doesn't want more selfish desire like having a child or becoming a full blooded elf. Yet this selfless desire comes from a selfish place of never wanting to experience loss and is a desire (with the winged lions help) becomes one she seeks to impose on others
Similarly to Thistle who is THE example of how selfless desires become twisted and selfish by the dungeon as he original wanted to protect the kingdom and makes sure they live forever, though even then this was a selfish desire imposed upon him by Delgal. Now after a thousand years of running the dungeon he is all selfishness that he views as selflessness.
Then there is the other notable former dungeon master, Mithrun. Once viewed as a pure and selfless man by those around him he harboured countless selfish desires that the demon exploited and consumed, leaving him with what he and others thought was just the desire for revenge. A selfish desire that manifested in a selfless form as he puts his life on the line to rid the world from demons. It's through this we see one of his most interesting traits, his sincere desire to reach out and help other dungeon masters, compared to all other interactions he is never this gentle or talkative with them, the other canaries quite clearly just want to kill them, but Mithrun, one of the very few people who can understand what they're going through talks to them. By the end of the series we also come to know that his selfish desire for revenge was in fact an entirely different selfish desire, to be consumed.
Not on to Izutsumi, she's a character defined by her selfishness, as a result of her upbringing she has to rely on and care for only herself but then she becomes a part of the touden party and is put in a caring environment for the first time, and in response grows to genuinely care for them as well, risking her life in ways she wouldn't have done before. Izutsumi acts as a pretty potent example of the crews selflessness with all of them (except Laios, who they defend her from his monster fixation) acting as parents to her. Marcille gives her the love and affection, both emotional and physical that she'd never received up until that point, and didn't even know she needed. Chilchuckvis the only one with actual experience as a parents and only parental figure who has treated Izutsumi well, he pretty quickly realises she is acting like a teenage girl and quickly adjusts to treating and caring for her as such. Sensei, who is pretty much all paternal instincts cares for her the only way he knows how and is the first person to adjust meals to her needs and desires. Izutsumi can be seen as a demonstration of environments shaping a person, her formative years being treated terribly made her selfish whilst this new caring environment allowed her to become selfless for the first time.
Building off the paternal instincts comment from earlier, that one of the two things that define senshi's selflessness. Sensei is both a deeply mature and deeply selfless character, as a result his selflessness comes in more casual and more adult forms. In respecting the autonomy of others and providing them with food. With these drawing from the two things mentioned earlier, his paternal instincts but also his experiences with starvation. His paternal instincts are best shown in the chapter after Falin is taken as we see inside his head, seeing he views Chilchuck and Marcille as very young and that it is his responsibility to feed them, and considered it a failing on his part if he doesn't. This paternal instinct also is what leads him to secretly resent Laios and Marcille as he believes Chilchuck to be a child and views them as exploiting him and putting him in harms way. His focus on feeding others is of course a result of his experience with starvation, he NEVER wants anyone to go through what he went through and is THE way we see him caring for people outside of the Touden party
Next up Chilchuck, a character who at first seems to be a deeply selfish ones, as he journeys with the group because he is paid to, not because he wants to. But then we do come to respect this, as dungeoneering is a job, a very dangerous one that, and like all jobs it deserves proper compnesation. Which is something he actively tries to facilitate in one of his greatest acts of selflessness, where after having experienced the selfishness of other races and their willingness to use half-foots as bait, he starts a union to ensure proper pay and workers rights for half-foots. Though rather interestingly our first exposure to it is through the deeply selfish Mikbell, who frames what Chilchuck is doing as an act of selfishness. We also soon understand that he deeply cares about his friends, more than even he wants to as he continues to travel with them even when the job is technically done. This does result in a moment of selfless/selfish desire as he seeks to trick the group into leaving falin behind because he genuinely cares about then, he thinks they're in over their head and wants to protect them, again selfless desire that is selfish, though he does come to respect their wishes.
Speaking of Falin. cause of her minimal time to be a character we're left what screen time she gets and that's a character defined by her selflessness, from her communication with ghosts, being framed as a mothrrly figure to Thistle and the acted that began the series, sacrificing her life to save the crew, and would define how they act going forward.
For Namari it caused her to leave and take up the better offers she'd received. A selfish act that Marcille in particular resents her for but is explained by both her backstory, she is trying to buy back the honour her father stole, which would hopefully repair the relationship between the Lord of the island and dwarves, a selfless act, and the establishment of dungeoneering as a dangerous job that deserves compensation, which is why Laios and Chilchuck who do view it as a job don't resent her while Marcille who doesn't view it as a job (a. she's very open about not viewing dungeoneering as a career b. ancient magic research is her goal, thus the particularities of dungeoneering never mattered to her) does resent her. We do see other moments of selflessness from wanting to know Kiki and Kaka's age so she can identify them if they need resurrecting and standing up for Laios. Namari's character is one meant to show selfishness, especially when your life is one the line, is not inherently immoral.
The other crew member who left as a result of Falin's death is Toshiro (Shuro), who immediately goes off to find a strong crew he is hopeful can make it through the dungeon as fast a possible to rescue Falin. In opposition to Namari he is someone who chooses selflessness over this own life, running himself ragged to save her, but it is this focus on her other his needs that causes him to fail, running yourself ragged will leave you unable to succeed, as demonstrated to him by Laios. Laios is a man he resents for various reasons but one of them being that he doesn't see Laios as sincere in his care, that he doesn't express his selflessness in a 'proper' way. That his happy go lucky attitude and focus on keeping himself health are proof that he doesn't care, when in actuality a) that's just who laios is b) Laios looking after himself is a form of selflessness because how can one help others if they can't even stand.
Laios sits in the middle of selfishness and selflessness, defined in equal parts by them. He is completely sincere and dedicated to his selflessness, willing to risk his life and go it alone to save Falin, he seeks non-violent solutions to deal with his human enemies, wanting to talk to Thistle and get him to respect the citizens of the golden kingdom's wishes and doing the same with Marcille alongside working to defeat the winged lion and putting himself on the line to do so, as well as becoming the king of the golden kingdom, which he clearly doesn't want. yet he also has a lot of selfish desires because of this and being an extremely autistic dude with basically no social skills he's viewed as worse than he is, both on his and other's fault. He loves monsters and his entire life is defined by his obsession with them, this obsession spawned from a resentment of humans how they treated his sister (he got over it, he was a teen). He seeks to examine Izutsumi, and while he means no disrespect or anything gross by it, she is a teenager and has some pretty serious trauma surrounding being treated as a circus animal. He disrespects Lycion's treatment to his suicidal body dysmorphia because it's a 'skin deep' appreciation of monsters. He views saving Falin as an opportunity to finally consume monsters, his selfish desires and his willingness to express then when it really isn't an oppurtune time to do so (dude, your sister's life is on the line) mean he is taken at his worst, viewed as literally villain by Kabru and the canaries. Laios as the protagonist of story with pretty clear themes of selflessness and selfishness shows one who is outwardly a very selfish person yet the moment you stop to look is a deeply deeply selfless person, even if he is bad communicating.
This brings us to his foil Kabru. Kabru pretty clearly defines himself by his selflessness, viewing himself as superior for it, believing he should be the one to conquer the dungeon and that Laios is unworthy based on his shallow understanding of him. This selflessness is further deconstructed as something very bad for him as similarly to Toshiro is clearly doesn't value himself like he should, not allowing himself to have selfish desires, with it being pretty clear this worldview is shaped by his childhood trauma, of seeing what the dungeon can do, his survivors guilt and believing he has a duty to prevent it. This brings him into interesting conflict with Mithrun and Laios. The former is someone is a person who literally cannot care for himself and must rely on others to do that for him. His lack of care for himself, unawareness of his own needs astounds Kabru, rather ironically considering Kabru's lack of focus on his own and his focus on Mithrun, who is noted to be looking better than usual thanks to Kabru's treatment by Lycion, indeed his focus on analysing and understanding other people in general can be seen as a form of his selflessness/care for others at his expense. The latter is a person who confounds Kabru, Laios is the first person who Kabru cannot understand, the first person he can't just casually befriend one so utterly antithetical to his own interests as Laios is fixated and loves the very thing Kabru is horrified by, monsters. This also shows arguably the biggest example of Kabru valuing others, his selflessness at his own expense when eats the monster food Laios offered him, looking like he might die as he does so. This horror and confusion causes him become fixated on Laios, he is a puzzle Kabru must solve, but also because of Kabru's views on monsters, selfishness and selflessness he views Laios as an active and terrifying threat that must be stopped. But underlying this is what Kabru refuses to acknowledge until he confronts Laios next time they meet, he wants to befriend Laios, something that horroifies himself, both cause this is Laios, but this is a selfish desire. Admitting to Laios is an admission to himself that he has a selfish desire and that maybe just maybe that isn't so bad and that doesn't make him a lesser person. This acknowledgment that desires are part of who you are is what allows him to reach Mithrun, Kabru developed a new desire, to befriend Laios and thus Mithrun can too. Kabru is very potent foil to Laios, a character defined by selfish desires and seen as dangerous because of them when in fact he is deeply deeply selfless, as he is character who looks down on selfish desire and values selflessness to his own expense, only to learn through Laios that selfish desires are not inherently bad, thus allowing Kabru to help others even more.
And last but not least is elves as a whole and in particular the canaries. Elves are this selflessness and selfishness theme on a societal scale as their racial paternalism means they view it is their duty to look after races whilst also not respecting them or their autonomy and this causing great harm, with the canaries and Milsiril being microcosims of this. The canaries are a force tasked with stopping dungeons a selfless act, though motives selfish as while some clearly do it to save lives, it's established that one of the reasons they do so is to get their hands on the ancient magic inside and their racial paternalism means they don't trust other races to know the secret of dungeons, which almost dooms everybody. We also see how many of the members of it are criminals, who quite frankly are selfish cunts, really racist to non elves and are more than willing to put shorter lived races in harms way to get what they want. Milsiril is this racial paternalism embodied, as she's dedicated her life to looking after children of other races, a selfless desire, but she clearly doesn't see them quite as equals with there also being the implication that this is the result of a selfish desire to deal with her own loneliness.
Desire is a key theme in dungeon meshi with selflessness and selfish being the accompaniment to it that really makes so much it so potent.
