What is going on here? I am not exceptionally well-versed in anime or manga tropes, but I think the “obvious” reading of this is a classic case of “unexpected juxtaposition creates humor.” That is, moving something from one context (“Demon Core,” radiation experiment, horrible death) into another (cute, anime, girls) creates something that feels novel and unusual

Ah, sir, I guess you’re completely unfamiliar with anime tropes. From absurd brutality to dark drama (much worse than your Titanic Ending and Futurama Dog), everything can be found in anime. Thinking that these are cute animations for teens and children is a big mistake. I, a grown up adult, usually dread when an anime plot is too nice to its actors and think if I want to watch it further. This juxtaposition is well-expected.

There's a lot of light and fluffy fare in anime. Even back in the 90s when I was used to sex, violence, drama, and strong character lore in my anime, I discovered You're Under Arrest and was a bit surprised to discover that it pretty much went nowhere, just an episodic series full of funny things for the characters to do. Especially surprising for a show about police officers, which in American media usually means it's a "procedural" with particularly dangerous criminals and high stakes. But in YUA the officers mainly deal with petty criminals and get up to wacky hijinks. More recent series, like Azumanga Daioh and Lucky Star, are pretty much just schoolgirls doing cute things. And maybe that's just the energy you need sometimes rather than, say, the horror and drama of Attack On Titan.

To paraphrase Brad Bird, anime is not a genre. It's a broad art form that encompasses all genres. This is a common mistake for Western viewers of anime; even in the 90s it was marketed to us as being all dark, twisted Liquid Television stuff. But yeah, actually, most anime is created for and marketed to kids and teens. In Japan, if you're an adult consumer of anime, your peers may wonder what the hell is wrong with you and why won't you grow up. (Manga is different; plenty of manga are produced for adult consumption, and these are fairly serious in tone, and may lack the fantastic settings or big-eyed character designs Westerners associate with the medium.) Adult anime otaku in Japan are viewed with the same bemusement and contempt we might have for, say, the grown-ass men who are fans of My Little Pony. This may have changed more recently, as the Japanese government has leaned into the idea of anime and manga being important cultural exports through its "Cool Japan" publicity program.