Ok, lemme just say something:it's not horrible, all right? The story it's actually interesting if you pay attention to it. The problem is the way the characters are used.
Most of the characters in this anime are underage (like really young, they're on the first year of high school wtf) but they have their bodies exposed EVERY SINGLE EPISODE!!!!!
The protagonist, Yuri, has her breasts exposed at least once on every episode....it's disgusting, it's unnecessary and ILLEGAL.
All characters have little to none personality. I mean, they're not interesting at all bro!!!! The only one that gets me curious about their past it's Sniper Mask. He's the only relevant person in there, and he should be the protagonist, you can't change my mind.

I know I said that the story it's interesting but...it's SO CONFUSING!!! It'll probably make more sense on season 2 (if we get one, that is), but I won't get my hopes up. We get introduced to a bunch of random information every second and NONE of them are explained further on the show.

Oh, yes, how could I forget it? WAY TOO MANY PANTIES SHOTS!!!!!!!!!!
As someone that doesn't enjoy Ecchi content, I hate that kind of fan service, but when it's done properly and in moderation I can tolerate it (like One Piece, we get some fan services here and there but Oda doesn't create a situation to show Nami's panties, for example). Besides, they're underage high school girls, man! Do I need to say something else to prove my point? I don't think so.

I saw some people talking about Yuri and Rika's relationship (Yuri: protagonist; Rika: her older brother who's a high school senior) and saying that they get weird vibes from them (inc3st vibes) and stuff like that, but personally I don't think it's true.
They never met in person to begin with (Yuri's goal is to meet with him, after all), they only talk on the phone and it was some pretty basic conversations (at least that I can remember). They do all kinds of crazy sh1t to be able to survive and meet each other, but they're siblings, you know?! Like, they're family in the real world.... I don't know, I didn't think so much about this, I just thought it was a standard sibling relationship, but honestly I wouldn't know how brother-sister relationships are, cause I only have a sister-sister relationship, and we're really close to each other, so....idk.

Final thoughts:
Garbage. This anime is horrible, it stinks, it makes my eyes hurt. Wouldn't recommend it to anybody, unless they're into suffering.
The story is poorly told and doesn't make any sense; the characters are uninteresting and shallow; and to put a cherry on top, there's exploitation and oversexualization of minors.
So, if you're into bad anime with disgusting sexualization of high school girls, watch this. But just know that the world hates you and if you like when underage girls are sexualized, seek help :)