Two steps I know:

1) Make sure you're on Nutaku's website (there are two of them - .com and .net so watch out) and click the "i" on the left side of the address bar. Look for flash and choose "Always allow for this site"

2) Go to "Settings > Show Advanced Settings > Content Settings... " then look for Flash.
Then click "Manage Exceptions".
Type "www.nutaku.net" or "www.nutaku.com" (depends on version you're playing 'SFW or NSFW') then choose "Allow" on the dropdown menu beside it.
Then click Done and restart your browser.

- - - Updated - - -

Forgot to mention I'm playing FKG using Chrome 57 (latest version) and the methods I've mentioned above worked for me.