It's the prequel to Kakegurui, but imo it does not add much new information/lore/plot/whatever you wanna call it to the anime show of Kakegurui. You follow Mary as a starting nobody in the gamble school, and just as with Kakegurui, she (and others) try to win games or gain advantages through some kind of scheme or cheating. This is the first shave down in my opinion. I might have different impressions, and I don't know if it is just the source material for this prequel, but the games and the schemes are really not interesting. Sometimes they are simple enough that the regular viewer figures it out if they think about it for a second, or the scheme/game is done at such a bullshit level that it doesn't even matter, the plot and story just move in favor of Mary by the power of bullshit.
The second shave down are the characters. Although they use the same or similar characters from Kakegurui, Mary feels very different(as it should since she is yet to experience everything), but she is at the level of a boring average character in the anime's world with a little bit more braincells and desire. Supporting characters that become her friends are medicore as well. One is just simping for her all the time without much reason, the other is also an average character which has little depth. I hate to say it, but I think the character I found so annoying and over the top in Kakegurui such as Yumeko, carried that show. If the voicing is less energetic and dramatic, it doesn't work. They need to be full on crazy.
The "crazy" shots are also shaved down. Where in Kakegurui you can see quite the number of dramatic close ups with sometimes glowing eyes and idiotic facial expressions, that is present in this prequel, but to a much lesser degree, and they are less dramatic. And that's a shame since those dramatic emotional moments went quite well with the ethically gray characters who would do anything to gain money when everything is on the line. Touching on that, that also slightly bothers me in this anime. Morals and ethics were almost nowhere to be found in Kakegurui. Yumeko was an addict that wants to satiate her lust for gambling, Mary was a bitch in it for herself most of the time, and you saw all that through the eyes of a wimpy MC. But in Kakegurui Twin, Mary has a feel of morality at times, a conscience for her friends, almost to wash her from the shit behaviour in Kakegurui. It's weird to see some good guys where first everyone had no moral compass, especially after you have seen regular Kakegurui. She and her one friend, maybe the other one too, for some reason have some kind of decency, but everyone else is just the worst, girls and boys, but especially the few boys in the show are just the scumbags of the earth.
Is this anime for you? This anime might have one purpose, and one purpose only, and that is to please the cosplayers that overrated Kakegurui, and give them more material and characters to group cosplay as some pseudo lesbians with suggestive kinks. Otherwise, you are better of just watching Kakegurui, the Kakegurui in its full glory, rather than this shaved down version.
