The problem with Mamoru is that not only is he a very obvious wish-fulfillment of a character that was created solely to appeal to Naoko’s own idealized tastes with which to vicariously live out her fantasies through - he’s also a character that’s defined solely
through that lens with nothing else going on about him. What do I mean by that? Well it seems he was created solely for shipping and eye-candy purposes to serve as an accessory to our protagonist Usagi and little else. He has little else going on as a character that can be divorced or defined outside of Usagi, he ultimately lacks both agency and presence. (Even
literally narratively lampshaded what with how much he tends to get kidnapped/brainwashed and has his role eventually reduced from main cast member into more of a supporting/background role in the 90’s anime ironically enough)
To be fair this is a problem that plagues nearly all the girls in the Manga/Crystal to some extent, where they truly only do exist to be Usagi’s cheerleaders and little else. But it’s worse with Mamoru because he literally has
nothing else going on his life in his life besides Usagi and Chibi-Usa. Take for example his aspiration/dream in life, the narrative claims he wants to be a Doctor, sure okay that’s nice and all but is he actually
passionate about medicine? Do we as the audience ever get a scene where we see Mamoru indulging in his passion for science or even just the concept of healing people? Even the girls get at least
that much when it comes to their often-stated goals and interests. What are Mamoru’s interests? What are his hobbies? Who are his friends? (Besides Asanuma who’s more just a hanger-on Kohai) Why does he not seem to have
any interest in life outside of Usagi or his Destiny and his whole entire world revolves around just her and that?
The sad thing is the premise and backstory of his character actually
is incredibly interesting and has a lot of potential to craft a really complex and nuanced character - I mean here we have a guy who’s an orphan with amnesia, who doesn’t have or remember any identity then the one Destiny is currently beckoning him towards. He thinks following this call will fill the empty hole in himself and will give his life meaning and purpose as well as a tangible, concrete identity to finally hang onto - that’s a
brilliant concept for a character and one that can lead to a really meaningful arc.
The problem is we never
get that from Mamoru… That potential for an interesting story to tell and an important message to impart is pretty much wasted, because Mamoru in both the Manga/Crystal and 90’s anime (though admittedly this is a bit better and actually explored in PGSM I’ll give him that) remains a static character throughout and he never really definitively comes to a resolution for his journey besides “You are the chosen one, follow that beckoning call of Destiny and submit yourself to it and you’ll be happy, don’t question it just know you were born the Prince of Earth and you will only
ever be defined as the Prince of Earth!”
When really an actual,
meaningful character arc would’ve had Mamoru questioning things from the start, internally asking himself if this is what he really wants, and coming to the conclusion that ultimately he needs to start taking control and agency of his own life and realize that only you yourself can create your
own identity and meaning in life , not anyone else for you. What shapes your identity and sense of self are the new memories, experiences and bonds you forge along the way, your past lived experience - be it coming into the world as a blank slate with no memories prior or a literal past life - do not define you. It’s how you
currently choose to live that does, and the only way you’ll be able gain that new sense of identity and self is by
choosing to actively engage with the world around you rather than insulating yourself to a single, lived experience. (That you yourself don’t even remember and are simply being
told to do, mind you)
That’s my problem and I think most of the fandom’s main problem with Mamoru. He doesn’t have a meaningful resolution or character development to the set-up for his story, and without that (or rather paradoxically, precisely
because of that meta narrative conception of him as a blank slate sort of character) he’s simply not very interesting. Because he has nothing else going on in his life or even as a very character aside from Usagi and the role/destiny he’s meant to fulfill. He exists for nothing more than just fanservice/arm-candy and shipping fodder, and the audience can tell.
The 90’s anime/Ikuhara at least
tries to fix this by giving him friends and a life outside of Usagi (And I will say, the creation of Fiore as a character concept helps out Mamoru
immensely, so kudos to Ikuhara on that front!) but this is offset by the fact that his relationship with Usagi in the anime seems even
more determined by the string of Destiny, (due to both their horrid development of getting together as a couple and the fact that even when they
do get together Mamoru doesn’t even seem to treat Usagi like a girlfriend most of the time) his increasing irrelevancy/presence as a character as the seasons go by,
and the fact that in a weird twist of fate he unironically turns into even
more of a Gary-Stu than even his original manga conception was meant to come off.
Seriously, I know he was originally conceived as Naoko’s “ideal man” but then why does it seem like at times that that’s what the
90’s anime is trying to portray him as? We could argue that Manga Mamoru isn’t a very
realistic portrayal of a man, (though admittedly neither is 90’s anime Mamoru) and in some ways that’d be correct because very few men are as sensitive, allow themselves to be vulnerable and admit their insecurities, or as willing to concede power and the spotlight to their girlfriends/wives like Manga Mamoru does. But unrealistic does not automatically equal a Gary Stu, 90’s anime Mamoru by contrast has been seemingly erased of all his flaws post-R and is held up as this perfect specimen of a man that has it all. I mean he’s wealthy, (note that Manga Mamoru’s financial status is never explicitly alluded to) owns
two cars, is the top student in all his classes, portrayed sophisticated and all the girls
and guys want him! Seriously, compare how many alternative admirers Manga/Crystal Mamoru has compared to 90’s anime Mamoru, literally only Beryl, Pluto, and Chibi-Usa while 90’s anime has Chibi-Usa
plus Rei, En, Fiore, Esmeraude, Mimette, Fish-Eye and Shiori! (And in the old Optimum dub we can even add both Amara and Michelle to that list.

)
To make matters worse 90’s anime Mamoru’s ascended Gary Stu-ness is frequently used just as a device to put Usagi down and make her the butt of the joke, all while putting a laser focus on their inequalities and incompatibility as a couple and making Usagi feel like she can never “measure up” to him, like she has to
earn his love cause omg he’s
such a catch didn’t you know! /s
What makes this even more egregious is the fact that we never even see Mamoru develop into this oh-so mature, sophisticated guy. Mamoru as a character in Classic didn’t start out that way at all, on the contrary he was an immature douche who’s favorite hobby seemed to be picking on middle-school girls and frequently losing his temper just because a shoe happened to land on his head. But come S and he’s all of a sudden done a total 180 to this calm, cool and composed epitome of sophistication? Sorry, but that’s a bit hard to buy.
It’s all these problems as a character he’s accumulated in both the Manga/Crystal and 90’s anime that gives him the well-deserved reputation as one of the “Scrappy Doo” characters in the fandom that he has.
By contrast, let’s look at one of the other male characters mentioned in the OP, Demande. Demande, despite vastly less screen-time I would argue is a much more fully realized character than Mamoru in either version. (90’s anime and Myu Demande only of course… Manga/Crystal Demande is a different story as he’s just an evil caricature) Yes he has an unhealthy obsession with the Neo-Queen, which you could argue is revolving his life around her and being designed solely for shipping purposes like Mamoru is, but there’s two important differences: The first, and arguably most important one is the fact that he isn’t defined
solely as a character via his obsession with NQS - he has other stuff going on his life! He grew up as the leader of an oppressed population who were banished to a miserable, desolate planet where every day was a brutal fight for survival, all for crimes they didn’t even commit. NQS is not the only person in his life (or even
the most important) he is also characterized through his close bond with Saphir and his care for his people.
His ultimate goal in life isn’t
just to get NQS but to also secure a better life for his people, and he’s (rightfully) filled with rage and notions of revenge towards what he perceives as his people’s oppressors, that subjected both him and them to a life of destitute poverty and withheld their rights from the planet they’re actually indigenous to, thereby creating a generational cycle of trauma that all people of Nemesis are a victim of.
The second difference is that he fell through NQS through natural means, whether it be a simple physical attraction or one fueled by his own inferiority complex, the point remains that he was not beckoned or forcibly strung to her by the call of Destiny. (Which automatically makes the whole notion of the Demande/Usagi ship immediately more appealing narrative wise than UsaMamo just on that basis alone) Despite being manipulated on the nose by Wiseman, he does not come across as a person lacking agency in his life like Mamoru does - he takes control of his own life, and frequently and assertively (if inappropriately) asserts his own will at all times.
Last but not least Demande actually has discernible flaws that results in devastating consequences- the narrative does not glorify nor baby him. He is incredibly naive, short-tempered, selfish, impulsive/short-sighted and frankly, just plain
dumb, and all these faults end up costing him one way or the other in the end. So between that and other important, defining relationships and goals in his life, a character who’s been shaped by and is dealing with systemic oppression and prejudice which is an incredibly relatable backstory, and whose relationships and shipping potential was
not formed solely through the “Magical Confines of Destiny,” yeah, it’s safe to say 90’s anime and Myu Demande comes off as a more fully realized character than Mamoru in either version does. No wonder he feels more fulfilling as a character to OP, that’s because he
is.
But to play devil’s advocate for a minute here, is Mamoru’s lack of characterization/agency really that bad? If you think about it he fulfills the exact same role women have been playing in men’s comics and shonen manga for ages - damsel in distress fanservice eye-candy whose live revolves around the Hero and whose only narrative purpose is be the designated “Love Interest” and Support and nothing else - the criticism he gets and role he plays is not all that different from those of female supporting characters in traditionally defined “men’s/boys media.”
Which makes sense considering Sailor Moon is meant to be a feminist role-reversal on traditional superhero tropes. Perhaps Mamoru doesn’t have much of a character or life outside of his role as “love interest” because that’s the whole point?
Would making him into a more fully realized character somehow “ruin” the more feminist message the franchise is trying to impart? (
I don’t think so, I’m of the opinion that the solution to under/misrepresentation isn’t simply to switch the genders around as a “tit-for-tat” but that the very
notion of dehumanization is bad all around and shouldn’t be applied to
anybody, also it’s simply bad/lazy writing all-together if a writer is unable to fully utilize all the characters they create to their fullest potential - but I see how it could be important for others for whom Mamoru’s character was a refreshing reverse take on overplayed and tired misogynistic tropes of women being only reduced to arm candy and “the prize to be won or the victim”)
To be fair, there
are certain aspects of Mamoru’s character I definitely do appreciate. I admittedly do like the blatant damsel-in distress role reversal in a genre so drastically lacking of them. I love that the very sparse characterization he
does get showcases him as sensitive, considerate, insecure and fragile. It helps impart an important message to the audience that it’s okay for men to be weak or ask for help, that femininity in men is okay and should be encouraged and supported more. Toxic Masculinity is a bad thing to idealize or expect from the “ideal man.” There should be more feminine-coded, soft versions of one’s “ideal man” being projected out there into the world as it shows that there’s no one right way for any man to be “ideal.” Masculinity should not be held up as the end-all-be-all of manhood and for that reason alone I adore the
idea of Mamoru!
…The problem simply lies in that that idea wasn’t as fully realized or fleshed out as it could’ve been.