For those who are interested/confused/intrigued by the game hanafuda and want to know/learn the rules of the game, or perhaps just have some free time, i recommend playing the game "Koi-koi Japan".
it's a digital Hanafuda card game that has actually taught me the rules of the game and made me love playing it.
The best thing about the game, in my opinion, is that there's a very accesible help system implemented that is quite beginner friendly. for example, it tells you what moves you can make or if you're wondering what card means what, or which combination to build.
so yeah, "Koi-koi Japan", it's available on Steam. it made me from someone that's slightly interested in Hanafuda after watching Summer Wars, into a guy screaming "Koi Koi !!!" at page 12 of this chapter when akira decided to call a koi.