This review is for the full game on Steam (this thread currently has only the demo). I've only played about 2.5 hours so far, may update this review when I finish it.
The core gameplay loop is primarily inspired by Slay The Spire. Deckbuilding along the the run, you get bits and pieces of character development and story as you go (including lewd scenes). Though, there's also a "battle" mode which I'm guessing is for those who want to replay missions for the gameplay without having to skip through scenes you've already seen.
I only played a few hours so I can't say how much content, but if I recall there was at least 3-4 missions/bosses. I haven't finished the first run/mission yet, but I did reach the boss and it took me ~2.6 hours, so I'd estimate, as a lower bound, ~8 hours of content? But there was also additional "hard mode" missions that were locked off, so I don't really know.
The gameplay here actually ended up hooking me, which surprised me since I play a ton of games and bounce off most of them. Even after I came to an H-scene, I kept playing just for the gameplay, and when I finished a second time and stopped for the night, I still wanted to keep playing. I don't expect this will be a game that I keep playing after I finish the story, but tbh that doesn't mean much from me, since I usually play games once and then put them down before returning to gameplay-focused big-budget stuff (like Monster Hunter).
Has voice acting in both Japanese and Chinese, but only for the women's dialogue.
Scenes are animated (not by hand, but using some tool, maybe Live2D, no idea really). I actually normally don't like these kind of animated CGs, I usually prefer static images, but in this game I found myself enjoying them.
Erotic content: You have full scenes, with kinetic novel style text and animated CGs, which play after certain battles or encounters. There's rape-on-defeat scenes, but it asks you and you can skip them, and it seems you can still see the CGs later in a different context. In battles, you have the shinobi girl onscreen, where she takes clothing damage as she loses health. She also faces towards the enemy, away from the "camera" and you see her butt bouncing nonstop lol.
Writing is good enough. Not super amazing, but I'm enjoying it a lot. Scene writing isn't always super erotic but it has a few good lines so far and the text is definitely an appreciated animation accompaniment. The tone is pretty lighthearted. Didn't notice grammar mistakes. Has auto-advance, textlog, hide text.