I mean if the issue is you being worried then my advice is “just go fuck it and write it” but if you mean you want general advice on characterization in writing I’ve got a few tips ig
- What are this character’s values? What is important to them? What motivates their actions?
I assume if you’re sending that ask to me specifically that means you’re at least vaguely familiar with the Fate serie, so these are the exemples I would use. For Barghest, that would be the ideal of a knight. For Morgan, that would be her rules, and more generally the desire to be fair and objective. For Castoria, the desire to avoid trouble/lay low and not make waves (or Minimize Her Own Suffering, whichever you want.)
- Has this character lived through any key events or have had any key experience? If so, what lessons did they learn from this?
Think Morgan’s “Uther got fucking murdered -> the only person I can truly rely on is myself,” Castoria’s “They even took my staff can’t have shit in Tintagel -> everything I love will be taken away from me eventually.” Not a Fate character but the first positive exemple of this I could think of was Xie Lian’s “at my lowest someone lent me a hand -> there is good in this world so I can’t give up yet.”
Based on these two things, what is the logical conclusion of xyz event happening to blorbo?
This should apply both for backstory things and things that happen in your story proper btw. If you write your blorbo repeatedly getting betrayed by people they trust, this SHOULD have SOME impact on them, even if their backstory doesn’t specifically include strong opinions on backstabbing.
All this advice applies to both original stories and fanfics btw.
Anyways hope it helps! Good luck!