The only thing you’re doing by linking Kubo to the creepy doujinshi is (even if it’s a small chance) risking the status of doujinshi and other such works in Japanese fandom on the whole. You’re risking getting the hard work of people who had NOTHING to do with this comic (which was uploaded without the permission of anyone involved) in trouble.
I highly doubt Kubo will do anything about this or react to it. Most likely she’ll ignore it like she does most of the other nagging messages she gets from overseas fans. She’s not going to take time out of her schedule to sue someone who drew a gross doujinshi, especially since the lawsuit would have to be on the grounds that it’s a book featuring copyrighted property, and thus would end up potentially condemning every fan who draws and releases doujinshi.
The legality of products like doujinshi are already a fine line, and continually bringing attention to them to the official creators, especially when the content of the books IS objectionable and doesn’t represent the spirit of the series, is a terrible idea.
There HAVE been series whose production companies have banned the sale of doujinshi in recent years for their series (i.e. Love Live, though I believe it’s unclear as to whether this applies to just doujinshi merchandise or if it also includes doujinshi themselves). Many, many fans make money from selling fanart and fan comics in the West and in other non-Japanese Asian countries, and it would be unfair if the country of origin for these series was denied that because of people’s behavior while other fans continue to profit.
Please think about the potential result of your actions before you engage in them.