Titles can be a tricky thing for writers to think of. But the writer is the best one to think of the title for their own fic, because they're the only one to know all the details about the story.
Some advice I can give is to think of the over-all themes of your story, or a few descriptive words about your fic. Maybe that will give you your title, since that works for my fics.
As a general rule, there are a few words that you'll want to avoid when it comes to titling Pokemon fanfics in particular: "journey", "legendary", "adventure" are common words used as titles for Pokemon fanfics (there are others that I can't think of right now), and if you use one of those in your title, possible readers might skip over your fic's thread.
Since you're going to be posting on the forums, you definitely want an eye-catching title. That's the first thing about your thread that members will see, so if your title catches their attention, they'll click on your thread and be more likely to read your fic.
It might also help to plan out more of your story, especially since you don't have a secure idea on the name of your villain, or even what happens after a certain point. By planning out more of your fic, you'll know more about it, which will help give clues to a possible title.
Hope this helps!
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