Cave Story Tribute Site Forums

From someone who has only finished one mod but worked on (and will eventually finish?) several others, this is my process:
Come up with a one-sentence story concept, a general idea of the mod's length, the mod's tone (comedic? dramatic? spoopy?) and a handful of gimmicks/ideas you have in your head. Then just... make everything else up as you go, for both gameplay and story. Map by map, cutscene by cutscene, textbox by textbox. Feel free to go back and change cutscenes/dialogue later, whether they suck or just contradict later parts.
That said, all of my mods' stories have been rather nonsensical, so take it with a grain of salt.
tbf most of my mods that have dialogue are also, well, very nonsensical
(see: restaurant mod)

This mod that I want to make, is currently *still* in the planning/early development process for (I started on March 12th of this year), is the biggest cave story project that I've ever worked on. And while I know I have the *ability* to make it, as most people who know me would know, I usually make challenge style gameplay-focused mods.

So, when this mod has a full-length story added on to it, with new mechanics and gameplay, it gets a bit harder for me since I'm not personally a writer.
That being said, I have slowly been able to string some small story bits together on the mod's first 'chapter'.

Also, the mod I'm talking about has not been revealed on the forums yet, but has been talked about a bit in the CSMC (including a playtest build thing for it), so anyone reading this who is there might know that I'm referring to "CELIA", which I still plan to keep mostly private outside of the development server I have for the mod.

Once the first chapter of the mod is ready, I'll hopefully release a trailer on the forums for people to see what the mod is all about. I wasn't going to release the mod in chapters originally, but I feel like getting a small sense of the story out first, and then continuing from there.

okay sorry for rambling about my mod, thank you for saying something @StudioDixel, it means a lot :)
I do it from scratch, and I use the process of "the ideal/best ___"
Like the best swordsman would be a serious character, not some goofy comedic character, and then I go from there
Of course this only really helps me come up with a character.
For the writing of the character itself, I just kinda imagine myself in their shoes and go with the flow.
That sounds like a lazy answer, but just imagining everything up to that point as the character then figuring out what to say next is really helpful for me.
Maybe you should try it, though my methods are infamous for being overcomplicated.
I actually do something very similar to Dixel in the beginning, think of a concept, then enhances it in your mind and think of the flaws and how it'd go, what would the story be and how to make it/adapt it to the gameplay. (Like "how do you introduce a narrator?" etc..)
Then I pretty much make the mod while thinking of fun ways to play around with the player and not make the map seem bland, a good half of the time, I just put notes into textbox and come back later to complete a cutscene or a dialog, what mainly matters is how the game will go and how to keep it interesting without losing the players, where that be: difficulty or boring.

Afterwards, I never took Cave Story modding story too serious, what mainly mattered for me was the level and or the concept, I'm just saying in term of story, I always putted that aside, still if I focused a lot on an aspect (like the narrator, a lot of thoughts put into Curly's Weird Crusade was how to make that guy) afterwards, as long as the mod is fun, everything should be fine.

For characters, I mainly think about what are his intentions and his beliefs and how he is. Afterwards, if you make it coherent, it would be okay.