A lot of people think any kind of single-player deck building game is a "Slay the Spire knock-off". What gives?
Have you played StS? This, Lust Evil, and Astral Lust all use the same card battle mechanics and sometimes even use the same names for cards and statuses. Or if the names aren't the same, the effects are the same with different names.
Well, it's currently the most renown of its genre... despite not being the first. Heck, it has been so long but IIRC Princess Waltz and the first Boob Wars were of that genre (with the latter perhaps not being a 'builder' but w/e).
It's not a shorthand for a card game, deck builder, or roguelike deck builder. It's when I can look at the combat screen and instantly extrapolate how to play, how enemy intents work, what strategies are most like to be good, and what kind of additional effects are going to exist, all because the game mechanics are based on StS.
There's plenty of porn card games, and roguelike deck builders that are not trying to copy StS, but this is not one of them.