Well first of all you should treat the story and gameplay separately. And the exact characters growths should be one of the last things you think of.
Now im no pro hacker or game designer, but i am screenwriter student and the first thing u need is an plot.
I dont have solid idea of what the story is because u didnt write a plot just a incomplete character sinopsis. However i can give u an example.
A young hobbit, a race of small humanoid beings, along with his companions embark on a quest to destroy the One Ring, and thus ensure the destruction of its maker, the Dark Lord Sauron.
Note. that there no names and the text just give u a very basic idea o what the history is about.
First the individuals or group of individuals, what he does or what he wants to do, and then why he does it.
You need the plot before anything else or u just gonna lost track of what the story is about and it will turn just in a mess of text.
When u have that, then u can do a sinopsis. A more elaborate form of a plot where u can talk in general manner of some of the points of the story.
The future of civilization rests in the fate of the One Ring, which has been lost for centuries. Powerful forces are unrelenting in their search for it. But fate has placed it in the hands of a young Hobbit named Frodo Baggins, who inherits the Ring and steps into legend. A daunting task lies ahead for Frodo when he becomes the Ringbearer - to destroy the One Ring in the fires of Mount Doom where it was forged.
Note. remember to just include the main character in the sinopsis and no one else.
Now to my next point. This should had come first but i needed to give you more context. There exist the main character and the protagonist, and they are not the same thing. You gotta decide which characters gonna be main characters or protagonists.
The main character is the one from where you see the story unfolds, normally the most easy types to find are the one that dont know anything of the world so things can be explained to the chracter and player at the same time. Ergo that why most main character are young, ignorant or innocent (Ej. Frodo)
A more easy example is eirika, at first you see the fe8 story from eirika point of view, before the split route. When the split route happens you can decide between her or ephiram to be the main character.
Now the protagonist is the one that move the story foward, sometimes the main character and protagonist are the same, and that ok, and while we can have multiple protagonist (Ej. eirika and ephiram) there can only be one main character at a time.
You can observe this at the route split at fe8 where u select a main character while eirika and ephiram are still the protagonists regarless of your choice.
Now after all this, if u still want to make all the work of making a good story i could help u out with it if u want.