You can definitely start writing without any prewriting or outlines, as long as it has correct format, grammar, spelling, punctuation, and whatnot. I suggest completely creating your character, describe his/her looks, write down some features that make the character unique (uniqueness of appearance, personality, personal items, etc), and describe the personality afterwords as best you can. For all this, I would just start writing as you think of it, definitely re-read and re-read again to make sure things are correct, and insert any stuff that comes to mind. If you were to do all of that, completely creating an original character(s) of your own, I am sure that you will have been inspired enough to start writing immediately or think of good plot lines and whatnot to form a basic outline (which you don't really have to write down, just remember!). None of this is really necessary, its just that, if you do this stuff, then you should be full of ideas to start writing your story. Outlines are never a bad idea, but are not always necessary. If you want, you can write simple ideas about the plot line from beginning to end, characters and how they are connected etc. If you want to cut some of the work needed to write a story, then I would write all the ideas in your head and write as you go, except I would stick with writing the character profiles. Just make sure you are sticking with the info, like don't umm, contradict yourself on some important information or parts of the story, unless it were some weird and sick twist. Just don't, for example, say a character is handicapped and in a wheelchair only to write that the character ran a mile before school, you know the common knowledge. I'll even give you a sample of one of my own characters:
Biography:
Prince Ryan Dante only remembers being on Earth since his birth.
Age: 20
Height: 5' 10”
Weight: 175
Hair: Messy black ear-length hair; or Messy Blonde/white ear-length hair; or Messy Dark-Red ear-length hair
Defined Features: A scar going directly over eyelid from eyebrow to very top of cheek, sometimes invisible, sometimes very apparent.
Gymnast–like body, with an additional 25 lbs of muscle.
Overly-skilled Swordsmith.
Master sword handler/Swordmaster. Most known for duel wielding specially crafted broadswords & Sabers or Samurai Swords.
Changing personality..
Often seen with a mixed black, green, gold, and maroon cloak and a broken heirloom pocket watch.
Family: Prince's parents are unknown, both to him and to others.
Unknown whereabouts of little brother.
Prince Ryan Dante does not actually know if he descends from a high-classed family, so despite his Princely title, he is not a Prince. Although certain items may or may not contradict this. (i.e. Pocketwatch, little brother)
Personality: Since Prince Ryan Dante is not a Prince, the 'Prince' in his name is often used as his first name. Because of this, Prince is his first name, Ryan takes up his middle name, and Dante being his last, He has been called Dastan once..
Prince has a split personality, thus describing why he has 2-3 first names. First off, Prince occupies a sliver of his soul and allows Prince Ryan Dante to see through the eyes of a leader. Maybe for this, he gains his Princely title.
Ryan is a half of his personality who's power and conscience derives solely from the Light and Ultimate Justice. He is a stern, but light-hearted person, who would never kill a person unless it were for penalizing the dark and unjust. Ryan has pure and utter Disdain for all evil and corrupt. He can be characterized by his messy white ear-length hair, and a Cobalt jewel pendant.
Dante is the other half of Prince Ryan Dante's personality. Dante is a surprisingly simple-minded person, who's thoughts are filled with pure blood-lust. He can be characterized by his messy red ear-length hair, willingness to kill his opponent, Survival instinct, and complete mastery of the Zanbato.
Since these three personalities make up Prince Ryan Dante, they are all linked in some way, whether it be Ryan's willingness to kill after sporadically succumbing to Dante's Darkness, or despite Dante's death wish, may it be Dante having spared his opponent, or giving in to his own light.
Lastly, Prince Ryan Dante does not know of his Saiyan abilities. It can remain this way only for so long, until his abilities awaken and fade in and out up until the point in which he learns to control this.
Sample Roleplay:
On the current day, Prince is walking back from his secluded training arena at dusk. He is taking each step leisurely, because he truly enjoys training. The one thing Prince feels is most rewarding is one's own self-improvement. In an instant, he stops abruptly to investigate the overwhelming power that is slowly, but swiftly crawling up his spine. Looking from the background, you could see a bright golden aura being emitted from his body, all while you could feel the intensity of the power as it was exuded from every inch of his body. At the moment in which the unknown power reaches its peak, Prince writhes in pain.
“Ahhhhhhhh!” Prince groaned and yelled in response to the power, “what...is this..powe-!” Prince questioned until he was interrupted by his need to drop to his hands and knees. This event soon came to an end, the young Prince crawled to his feet and proceeded to walk home.
Upon entering his home, the moment he came to his bed, he had just collapsed and slept through the night due to low fatigue from what had happened on his way home.
Not a moment after the sun began to rise, Prince was already on his feet and gathering his items to start his weapon training for the morning. Building his check-list, he picked up his Twin Broadswords and strapped them in an X formation on his back. Secondly, he had remembered today to grab his newly crafted Sakabato and Suguta Tanto: Hochogata combination and attached them to his belt on his right side. He then set out on foot to journey to his training arena that he enjoys being in.
As his walk came to an end, he stepped foot in his training arena and dropped all of his items except the Twin Broadswords. He then took his stance, raised his Twin Broadswords to their normal upright form approximately two feet apart, with the left arm slightly slanted towards the Right Broadsword and lowered about a foot, and began training.
His training for these weapons included: focusing his Ki, quickly charging his Ki up to par, and attempting to push his energy throughout his Broadswords, enshrouding them in a bright golden aura while sustaining that form in hopes of someday achieving a skill similar to the Legendary Spirit Sword, except replacing the magnificent force with actual swords for the time being. This had continued as he occasionally broke concentration and restarted the sequence over the course of several hours. From there, he would switch out his Twin Broadswords with the Sakabato and Suguta Tanto: Hochogata combination and practice general dual sword techniques until the sun would start to set.
I really hope any of this helps you a bit! I'm not even an experienced writer, that's just the stuff I know, just take in what I said and grow on it!