Just going to quote Alice here since she did a pretty good in-depth analysis already, and just say what I agree and disagree with.
You explicitly use characters of other series. Their names/personalities/powers and etc are reused. You explicitly label your story as a fanfiction too.
100% agree on this one. A fan-fic is something that just unashamedly uses the exact likeness of characters, scenario, or locations and events. However, it tells it's own story.
You actively copy plot points and character developments of other series. Sometimes you straight-up copy parts of dialogue even, maybe only changing a handful of words.. And in the worst cases, you copy entire chapters, changing only names, and phrasing here and there.
This can be hard to identify, but it's not impossible.
I disagree with this somewhat, and that "somewhat" is only there (as opposed to disagreeing completely) because the OP did not add the option for what you actually just defined here, which is plagiarism.
Yes, what you defined here is somewhat disguised plagiarism. It is different from a copy-cat in that copy-cats utilize a few concepts and similar scenarios but go in a very different direction and implementation with it. A good example of this would be "The Beginning Before the End," which is a copy-cat of Mushoku Tensei. The parents' background might as well be 100% identical to MT, and the early scenarios are basically what would have happened in MT if the main character had a better personality, but at some point around the end of the introduction when it's moving into the inciting incident it diverges completely and really goes off in it's own direction.
You're just working in a similar space that another work had explored before.
An Otome Game Reincarnation novel is surely gonna be inspired on other Otome Game Reincarnations. While the first person who did it was original, it's extremely unlikely that another person will have this idea without first entering in contact with other Otome Game Reincarnations.
Same thing for most medi-fantasy stories, or ABO stories or whatever. You like stories, you use them as inspiration to make your own thing. Your own twist on something that many people did before.
Yeah, I pretty much agree with this one too.
So, yeah. To sum up my assessment, 3 categories is not quite enough here. There needs to be a 4th added in the middle. There's fan-fic, plagiarism, copy-cats/clones, and then there's inspired works. Maybe even a 5th. There's blatant plagiarism and then there's disguised plagiarism.
Another concept to think about is spiritual successors, which are a strange mix between a copy-cat and a fan-fic that very intentionally walks right up to the plagiarism line without crossing it, and openly admits that they are doing so in order to try to capture the same feel as whatever it's claiming to be a spiritual successor to. Usually, these kinds of works are done in terms of large intellectual properties that are owned by corporations, and are made by the people who worked on the original IP themselves but have since moved to a different company and thus can't use the name or likeness anymore. but, since they still want to develop something with a similar concept, they make something with changed names and likenesses and a few changed concepts, but has a feel very similar to the original.
(One of my favorite spiritual successors is a game called Another Eden, which is a spiritual successor to Chrono Trigger.)