This is my favorite koi koi app. It’s clean and simple. Bug free (mostly).
However I do not read Japanese so it can be tough. There is no English. I wish there were.
Also I have noticed that if this is the last app I use before bed, my battery will be completely drained by morning. I imagine it has to do with the way the ads are served. It’s a major flaw. Make sure you exit the app and close it completely to keep this from happening.
Last but not least I would absolutely pay to remove ads, but there is no option to do so.