Hmm i don't exactly have a set step by step system on making characters but first i read about a universe and do an google image search for something fitting on that theme and build my character based off of an image i like. Later the characters appearance may or may not change as the character is built. Usually images help me imagine how a character would act and what type of a person they are. if i put it in steps my process is rather simple.
1) Read some lore about the universe that character is supposed to be from or create your own universe. then decided what they could do in that universe and what would be their end goals.
2) Do an google image search on characters that would fit into the universe and the chosen role of yours.
3) once you have found the image you can use that if you wish to build a characters personality maybe a super power if they got one. specialty... an image shows ALLOT about a character.
4) With personality and ideas on what your character is good at and their end goals in place just write it all down in categories and adjust as needed to fit better with some aspect of your character you want to be more prominent.
5) now its time to add detail and explain things much more clearly so others may understand your character. this is where you can also adjsut the characters appearance if you don't want to use that image or just stick to what you got in your image.
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Example
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Universe: Boku no hero academia
What they gonna do there: A first year student...should start off pretty strong and grow even stronger as time goes on
So this is an BNHA character the universe has its own little sets of rules a character should follow.
Quirk: So i found an awesome image of an liquid nitrogen girl and will use that. it already has the heroes outfit in it so you already know the loadout of support gear your character would use.
Now comes the harder part of actually building the character. for me its deciding their name is always a challenge.
Name: Tracy Carter
Superhero name: Absolute zero
Nickname if there is one: Frosty
Age:15 ((since its supposed to be a student so they should be relatively young))
Gender: Female ((the character can be based off of a male char but then you would have to build your own appearacne later))
Appearance: ((Now comes the appearance. this is where you decide if you wanna use the image or write your own. in this case im using the image Which will be at the bottom of the post.))
Personality: ((i have an idea of her abilities and what effect they would have on her life style which in turn impacts the personality.)) Tracy is a polar opposite to her Quirk and is doing her best to always be friendly and cheerful which at times can be very difficult. Many fear to even go near her and way less even want to talk to her. This reluctance to interact with Tracy is slowly being affected by as er usual cheerful nature can often times turn stone cold and emotionless. almost as if the person no longer was a person but a machine.
Quirk: ((so we know its liquid nitrogen based and we can see all the gear. lets do some research on what liquid nitrogen is and what its useful for.))
Liquid nitrogen: The user of this quirk is in total control of the nitrogen they create as the breathe in the air and convert it to liquid state within their body which then is leaked out through the skin. Usually the nitrogen is stored in tanks for later use the user has limited supply and has no control over how much or how fast they generate the liquid nitrogen. The user can freeze boil and control gaseous form nitrogen at their will. Freezing is especially useful for making nitrogen ice swords armor or shells for the cannon. liquid state is good for do cold burn damage and be non lethal in general. Gaseous form could be best used to suffocate fires or smoke out a villain by removing the oxygen content int he room they have hunkered up in. Lastly the users body temperature at the core is usually at -240 Celsius but can reach the absolute zero and the skin temperature is -196 degrees Celsius, the boiling temperature of liquid nitrogen.
Bio/History. ((This is another part i struggle a little with so i usually leave it vague and have it form in the background as the character develops and reveals it bit by bit.))
Born int eh icy depths of Siberia Tracy was unusually adept with the cold and loved it way more than even her mother that was supposed to be the towns nicknamed ice queen. The discovery of her quirk truly came in as a shock at the age of four when one day she woke up in a room flooded by nitrogen and frozen to the point it looked like the room had its roof torn off in a blizzard. From that day on Tracy's interactions with people wend to a decline. at the school people avoided her even the local bullies were terrified of her. as time passed She heard about a new heroes school being built in America and was accepting international students. Thus after a long time of thinking and planning she set off on a new path. To prove to the others that she could be a hero and help people despite the innate danger of her quirk.
So this is how i create a character and an example of a simple character that has plenty room to grow and expand. I personally don't like laying out every tiniest detail before hand and leave no room for character development because all of that would change the moment other people and their characters come into play. They might save Tracy from turning into a stone cold hero who's set on the path to becoming a villain or they might drive her further into the rabbits hole and make her into a villain way earlier than planned.
((lastly here is the image i promised))