The clips of space are from pixabay and marked as "CC0 Public Domain. Free for commercial use. No attribution required" so they are 100% free to use (although I would like to note that I didn't just use the space videos in their raw, I edited them in a manner similar to those on /r/shooting_stars/ ). What I meant by 'mostly' was that there is a couple seconds of a clip of an anime character.

However I feel that the video as a whole is transformative enough to qualify as fair use. (although I may be wrong on that)

So I guess I will clarify my question more:

The visual space part of video is made from content which I had the right to use (the space clips are public domain), and have I edited the space clips so that they are something very different from the original. So, can I make a claim against a video for the part that includes the content I created (the space scenes)?

(Side note: I'm going to try to contact the channel first before I attempt the takedown, as it might just be where someone stores videos they like as backups, and I don't want to be a dick. I'm only asking this as a worst case scenario where they pretty much give me the middle finger.)

Also, thank you for reading my question and responding, I really appreciate it.