It's like as if someone was attempting their own version of Do You Love Your Mom and Her Two-Hit Multi-Target Attacks?. The dates line up. That began as a light novel series in 2017 and got an anime adaptation in July-September 2019. This was serialised online on the user-generated novel website Shousetsuka ni Narou from December 2019 onwards.

DO YOU LOVE YOUR MOM etc. = a teenage male protagonist (Masato) is sent to a fantasy RPG world with his smoking hot mother (Mamako) and is put in sexy situations for tasteless comedy. Masato's aghast, but loves his mother and sticks with her, ending up the sole boy in a harem/party of strong girls. Distressingly for him, though, he can't show off his hero skills because his mother got all the isekai superpowers and keeps one-shot-killing their enemies.

ONE-HIT KILL SISTER = a teenage male protagonist (Asahi) is sent to a fantasy RPG world with his smoking hot sister (Maya) and is put in sexy situations for tasteless comedy. Asahi's aghast, but loves his sister and sticks with her, ending up the sole boy in a harem/party of strong girls. Distressingly for him, though, he can't show off his hero skills because his sister got all the isekai superpowers and keeps one-shot-killing their enemies.

I enjoyed both shows, even if both got a rough ride from certain English-language reviewers. They're not clones, incidentally. They're very different in some ways, although the similarities are undeniable.

Asahi-Maya's incest-teasing is more obvious and less funny. The "joke" is simply that Maya's in love with Asahi and wants to cuddle him, marry him, have sexy fun times with him, etc. He keeps saying "no". That's it. In contrast, Mamako and Masato both believe in traditional mother-and-son relationships and are both horrified by the show's sleazy contrivances. There's just plenty of room for mischievous misinterpretations of Mamako's conventional-but-extreme maternal love, which she lays on so thick that she embarrasses Masato.

Do You Love Your Mom is also a better-looking show, although they're both surprisingly well made and visually popping. This show's fanservice is cruder (although less tasteless) and outright unattractive in its beach episode.

The big difference between the two shows is what they're adding alongside their central pseudo-incest comedy relationships. Do You Love Your Mom digs deep into its "adventuring with mum" concept and finds all sorts of fun iterations of it. It's focused on that theme. The results are quite interesting. This show, on the other hand, has nothing much to say about siblings. Asahi and Maya are likeable (despite Maya's craziness), but there's nothing intrinsically funny in the idea of adventuring with your sister and the show isn't even really trying in that direction.

Instead, it builds genre-aware gags around Asahi himself. He's initially delighted to have been isekai-ed and expects the traditional isekai cheat-level superpowers. Nope. Comedy failure. It's Maya who can punch out dragons. Asahi's just an out-of-shape otaku who's never touched a weapon in his life and keeps expecting the world to behave like a video game. Hah. What's more, he's given credit for Maya's deeds and given an appropriate RPG level, but fraudulently appropriating an undeserved level or rank is a capital crime in this world. They can't just let Maya do all the megakills. They've got to keep pretending that Asahi's the strong one, even when they're facing Maya-level foes. This is reasonably funny and inventive. I enjoyed it. (Mind you, Asahi gets better at concealing his weakness and even becomes capable of sneaking the odd victory with his few weak skills.)

I like the cast. Asahi's situation is scary enough that to warrant his place as the show's protagonist, despite all the wackiness. Maya is an incest-oriented nutjob who'll annihilate anyone who even looks funny at Asahi, but she's also cheerful, supportive and affectionate. (Too affectionate.) I liked her. She repeatedly saves Asahi's life, listens to him and always does what he asks. Then there's Kilmaria. She's a general in the Demon King's army, but a good match for Maya and eventually our heroes' best evil stripperiffic friend. I genuinely liked the relationship between the three of them. There's also Sophie, Gloria and Kuon, each with their own RPG character class, skill set and personality defects.

The show's fun. I enjoyed it. It's a decent companion piece to Do You Love Your Mom and Her Two-Hit Multi-Target Attacks?, with enough differences and strengths to be worth watching in its own right. It's less memorable than its predecessor, but that's partly because it's less tasteless. (However, you might have trouble convincing someone of that if they've seen this show's face-in-boobs scenes...)