How do i download from 9anime

yt-dlp supports a ton of sites (not just youtube). It's a command line program but there's a lot of different GUI frontends, like Seal (Android) or Parabolic (Linux and Windows).

I don't know if it supports the site you wanna use (someone else already said that 9anime was shut down, so the site you're using is likely a fake and you should use another one) but there's this list of supported sites.