The author behind that and the author of the Mushoku Tensei: Jobless Reincarnation series both commented on the matter after the manga’s’ cancellation.
Among the many titles that had their characters parodied with a dark twist was That Time I Got Reincarnated as a Slime.
Slime author Fuse responded to the apology in a blog, a portion of which mentioned how important a character’s image is to an author.