Boost has features already available to block various communities and sites. As much as I would like to see Lemmy implement and enforce a robust tagging system like some sites were probably never going to have that.

You could also probably minimize your exposure by blocking the Japanese character set and popular sites such as pixiv, deviantart, *booru and catbox. But anime is mainstream now, just look at McDonald's clever advertising scheme.

But if you would like to pioneer that feature, I would suggest posting your feature request to lemmy's GitHub since this is a bit beyond the ability of a client. And perhaps learn a new skill and implement that feature yourself.