Even without reading the source material and spoiling anything (and also without reading ahead: right now only the first chapter of this manga is translated) at this moment my suspension of disbelief is a bit strained, but it is not broken. I have a plausible explanation for everything that I see in this chapter.
Both Kaori and her new boyfriend (Katsuki-san) do not seem to know that the main character (Harukaze Reito) is an SSS-class adventurer? — that might just mean that dungeon exploration here is not broadcasted (livestreamed) for the world to watch (unlike, for example,
the livestreamed adventures in “
Aparida” or, say, in “
Yamiochi Yuusha no Haishin Haishin”) and thus the top adventurers are not celebrities.
Kaori says that being an adventurer is an unstable job? — well, Kazuma in the well-known “
KonoSuba” has already said almost the same thing, adventurers are basically glorified
freeters. And here Harukaze Reito says himself that he had to study investment before he earned “enough money” for his future life with his beloved.
Why does an adventurer not earn this much money normally in the first place? — we might (and we probably should) suspect an exploitative system that feeds on the hopes and dreams of the youth by promoting the success of the selected few, promotes the prospects of future wealth as opposed to the current income. It is sad, but it is believable. In the so called
real world it is said to be happening, right now, in some very different areas, such as
in drug-dealing gangs and in academia. Of course, the drug-dealing gangs make an even better example because they also come with the “get rich or die trying” mentality that is likely similar to what's necessary for the adventurers in the dungeons. It's not just a low income job under a disguise of some
Stanford marshmallow experiment (though perverted by the uncertainty of the delayed outcome), it's also life-threatening.
Why does a random staff member of the adventurer's guild has the authority (even when off-duty) to erase the registration of any adventurer? — like the very first page of the manga has already said, guild members are basically law enforcement officers, that's why they're given much authority. (This one let his authority cloud his judgement a bit, treated it as a tool that silently begs to be used in any conflict, like the police officer who performed
the 2009 arrest of Harvard professor Henry Louis Gates Jr. and never expected to be then reprimanded by the president of the United States of America. This is also a good example of how a certain character of a story may be near the top in his own field of expertise, like a professor in academia or an SSS-class adventurer here, but still be a random unknown nobody for the law enforcement officer who does not care about that particular field at all. Albeit a bit strained example because a cop not interested in learning any names prominent in academia is understandable, while a guild staff not interested in learning any names prominent in successful adventuring makes him quite a fair bit of a lazy jerk.)
Is it unprecedented that the initial sadness of the breaking up with a girl who leaves the main character because she's chosen a man who is from a slightly upper management (and who also has a slightly better apparent income) is closely followed by them forcing the main character out of his job? — nope, even in the world without any dungeons the exact same thing happened to the protagonist of “
Kimi wa, Nina Janai”. (The likely reason behind this is that the successful couple hates the thought of having to deal with meeting the man later accidentally on the job, or something like that.) It should be remembered here that the protagonist of “
Issho ni Kurashite ii desu ka?” has also lost both his girl
and his job at the very beginning, but the cause-and-effect there is almost the opposite (she's chosen an “elite employee”
a week after the protagonist got fired, and also that “elite employee” was probably not related to the protagonist's job because worked elsewhere).
Why does Harukaze Reito not retaliate with magic against Katsuki-san? — like the very first page of the manga has already said, guild members are basically law enforcement officers, and thus it would have taken a very special kind of a protagonist to shoot a law enforcement officer and then to start his own personal guerrilla against the whole system, and all that for a girl who clearly does not even like Reito anymore. Also we should not automatically assume that adventurers can use their magic outside of the dungeons (for the record, at this point of the story we are not even shown
any magic except in the name of the “magic stones” where that word still might have been used figuratively, hence the dungeons might still be the place of magicless melee, like in the well-known “
Sword Art Online”, until shown otherwise in the next chapters when Hiragi Karen starts her very first adventure in the easiest dungeon) and that the guild leaves its “elite staff” without any protection against the magic of the very same adventurers they apparently govern.
Why does Harukaze Reito eat some cup noodles, is he dirt poor now? — nope, he probably still has his “enough money” for the lifetime, he must have not been really able to spend all of it in just one drunk night. He just does not really care about eating junk food while grieving, like Otosaka Yuu in the seventh episode (or in the 30th chapter) of “
Charlotte”, for example.
Why does the clan led by Harukaze Reito (“the Twilight Tea Party”) not have any contact information of their own leader and also why do they assume he quits adventuring voluntarily? — because that's exactly what he said he was planning on the 14th page (“to quit being a dangerous adventurer and live peacefully with Kaori”) and thus he might have dropped some hints to them already, and then would probably not let his honeymoon to be bothered by phone calls from the people he was willing to leave behind.