審美的転生注射, Zazan

The whole manga/anime series is like that. Repeatedly. [SPOILER ALERT] You quickly go from "Typical shounen protag goes on a quest to find disappeared dad, meets companions along the way" to "holy cr*p all these people strong enough to make it to the hunter exam (e.g. Special Forces tough bare minimum) are getting slaughtered left and right, and the creepy murder-happy clown is a pedo".

And then you notice that the world is full of other Warhammer 40000 Death World-level lethal places, and extremely powerful and dangerous people and organisations are either in charge of much of the world or rampaging through it with impunity because they're virtually unstoppable by anyone not on their level (the dysfunctional master assassin family *almost* comes across as not that bad by comparison because at least when they're not on a contract most of them usually leave the rest of the world outside their estate alone - hired personnel and family members currently in disfavor are fair game though).

And then an invasive species from the mostly-unknown Dark Continent shows up, and starts eating everybody, quickly ramping up in power to the point of becoming an existential threat to humanity. It gets so bad that the good guys have to use their world's version of a dirty nuke to take out the threat.

And then it turns out that said invasive species is probably the LEAST terrifying known lifeform from the Dark Continent, which is actually over 95% of the planet - the Known World, which is about as big an area as Earth (same continents, different placement), is just a small archipelago in the middle of a lake. The place and the things found there are the kind that would give HP Lovecraft nightmares, and just going there is akin to playing russian roulette with the survival of humanity (notice a theme here?), and now some genius (actually several) just organized one of the largest expeditions to the place ever seen. Oh, and there are plenty of the aforementioned extremely powerful and dangerous people that are taking part, and even then the chances that they'll survive mostly intact is pretty slim.