Jjune just posted to twitter saying it is not his/her image, and confirmed that it is not a patreon reward either. Seems to be someone imitating jjune's style, then.
Someone else sent the publication and he responded in this way, my mistake. I was sure it was his drawing >_<
@Dimension252525 Kind of a haphazard accusation to throw around, especially with zero proof. I recommend you watch yourself next time.
JJUNE shouldn't have to do this in the first place, and it's kind of humiliating to the original artist even if they're a close imitator of their work.
I have met a lot of people at Pixiv who publicly owned Patreon. I thought this was one more and that it was necessary to give the artist the corresponding credits, if they were stolen.