Does anyone ever try writing Fanfiction but can’t seem to make dialogue that feels natural for the characters? If so, How do you deal with it? Do you keep going with the plot and come back later to fix it or focus on it and don’t continue until it’s right?

Ah, I know this tragedy well. The best thing I find that helps me with this is going back to the original material and re-listening to some episodes or reading a specific chapter of the manga. Better if you can find a chapter/episode that relates closely to what you're writing. Otherwise if it's original material, then I would come back to it latter if it's that bad of a struggle.

Thanks Xehanorto! I been re-reading issues so i can get the dialogue down but i feel i can’t do the characters justice! Do you think it helps to nail down a character’s personality before writing Dialogue?

It's definitely good to know what you're going for with a character before you try to write their dialogue. I've found this has helped me a lot when writing smut fics or Alternate Universe fanfics.

I just write whatever fits the story and then go back and change the dialogue to it them better

Nice! Thanks for the Help!

"an den they touch butts!"

There a strong line for you.

I know this pain too. Some characters are easy enough to write if they have a simple personalty to understand (Harhui Suzumiya, Double-D, Sherlock Holmes and Super-man, to name just a few) but it's often a challenge for a majority of others, especially when it's a topic the media doesn't touch on, try and get into the character's mind set, and check their reactions in cannon to similar events if possible. Likewise i find trying to match their style of wordplay helps, dictionary.com is one hell of a tool to use when trying to find just the right word. Of course, a secret tip of mine, is going over historical quotes to find witty lines if my intellect fails me.

It can depend on how much "like canon" you want things to be, but if your original source isn't a book, but a comic, tv show, movie, etc, I recommend taking a scene from that, and trying to convert it directly into text format first, so you have a more direct comparison.