Naughty, Naughty, Little Adventurer!
While your character spends all of their in-game time battling monster and demons, chances are they may also be battling against a naughty little secret that my do irreparable harm to themself or to others if that secret ever got out.
Secrets are one of the backbones of any good role-playing game. Whether it be a secret the BBEG (Big Bad Evil Guy/Girl/Person) is keeping from the adventurers, a secret the DM is keeping from the players (for now), or even a secret your party may tell the BBEG in order to hide their tactics.
But it is the secrets that your character keeps to themself (and maybe the DM/GM) that have the biggest impact on your game's storyline. Not to mention the impacts on your character and your fellow adventurers.
Answering this prompts for your character can be both a lot of fun and quite terrifying at the same time. This secret could be about your character's identity, something naughty they did earlier in their life, covering for someone else's naughty deeds, or maybe it is about a secret love.
These secrets and numerous others may seem reprehensible to your character (hence their need to keep it secret) while others may find them quite innocent by comparison. The exact opposite could also be true. These secrets can be kept or shared to protect your character from being harmed by other, or to protect others from being harmed by your character.
Cautionary Note: if you, as a player want a truly cathartic experience, you might even consider giving one of your own secrets to your character. Be very careful though as the other players reactions (hopefully via their characters) may come across as the exact opposite of what you as a player are hoping for which can be damaging to your own mental health and possibly your relationship with the other players.