Context: my sibling uses their tumblr to post/reblog/whatever Zosan fanart. I'm not into BL or One Piece, but I know how much joy the ship brings them, and bc they're one of my biggest cheerleaders, I'm always happy to let them share with me about this kinda stuff.

Well, today, my sibling told me someone was accusing them of stealing artwork and trying to pass it off as their own. Mind you, my sibling always credits artists, UNLESS the artist cannot be found. Even still they are always happy to properly tag once the artist's been found. They rarely cannot find the original artist as they do extensive research to look for who to credit.

Now, I haven't been on tumblr in a decade and even then didn't use it much, but this is my sibling's happy place, and I don't take to people harassing my loved ones. So I commented on the post. And then the accuser deleted my comment (comment I made before it was deleted shown below). They also messaged me accusing me of being my sibling's alt and immediately blocked me before I could clarify anything. And that upset me bc my sibling already isn't a confrontational person and tried to rectify the situation, but this person completely dismissed my sibling's explanations. On top of that, can they really not fathom that people have loved ones that would come to their defense when someone's harassing them? So I messaged them under a new account telling them that I'm not an alt and to stop harassing my sibling. And they blocked me again. So I made another account to tell them just to delete the post, but obviously that fell on deaf ears. So now I'm asking anyone that'll listen.

I don't care if I'M wrong, but my sibling is not. My sibling found a safe space to enjoy their niche interests and share with others, and I do not appreciate someone trying to tear that down. So can anyone give me advice on how they would handle someone harassing a loved one?

Screenshots for context. therogueheart is the one harassing my sibling. As you can see they're also harassing lala on other people's tumblrs too.

ETA - in my not so humble opinion, therogueheart's argument is baseless anyway bc, as my partner pointed out to me, fanart has no legal copyright in the first place bc they are already drawn without permission of the people that created the characters in the first place. We credit fanart out of appreciation for the artists, not bc it's legally required.

ETA - please remember my sibling has already taken their own course of action. Before I even got involved, my sibling has already taken down the posts that weren't reblogs. My main focus here is that the fanart in the screenshot could not be traced back to its creator, and my sibling just wanted to share it bc they liked it and thought you all would also appreciate it. They never claimed it as their own, even in the screenshot it says they tagged it as #not my art and #i don't know who the artist is