Perfect, Lundgren, you're all set, apart from a little detail: your Computer Science optional class level is equal to twice your Computer Science skill, and that's all. To increase your optional class score, you need to increase your skill. Now, rules explanation time!
The general rules are pretty straightforward. 1D10, you must roll under your attribute or skill. Emotion checks are the odd ones out: you must roll above your Emotions to keep them in control. (10 is always a success.) So high emotion is a double edged sword: sure, you get more powers. But you are also more emotionally vulnerable. If you like to play an emotionally vulnerable character, go ahead. If not, then between 6 and 8 is a good score.
School subject work differently. I am not really familiar with the grade system... The system is made for a grade from 0 to 20, like in France (cause it's a French tabletop RPG). The base system is, when going to an exam, you score in the subject your score - 2D10 + 10 + bonus for being extra studious (or - penalty for not studying seriously). It is used to make a grade between 0 and 20. So I need the help of someone more familiar with the grade system to convert that part.
Then, since you will be expected to fight against demons, here are the rules for combat and magical attacks:
Combat: You start by rolling initiative. 1D10 + Dex. Higher rolls go first. In case of a tie, higher Dex goes first, then higher Fitness. If both are equal, reroll to see whom goes first.
Any character attacks once during his/her/it's turn.
The attacker rolls for the attack using his/her/it's Brawl skill (or combat sports, if he has it). The defender rolls either his/her/it's parry skill or his/her/it's dodge skill to avoid the attack. The higher success margins wins. In case of a tie, a defender's success or if both miss, the blow/shot/spell fails to connect.
Multiple attacks: Any attack after the first that a defender has to try to avoid gives him/her/it a -2 cumulative penalty. So if your magical girl is attacked by 3 demons, the first attack is resolved normally. The second one gives a -2 penalty to the magical girl defense. The third one a -4.
1: Characters with 7 in Combat Sports can use it instead of parrying. Also, they can use 2 melee attacks per round, and suffer only a -1 cumulative penalty when faced with multiple attacks.
2: A magical girl with the Combat Prowess power 5 to 7 gets an extra attack and defense, A Combat Prowess power of 8 or 9 gives two, and a Combat Prowess of 10 gives three extra attacks and defenses.
3: Using a ranged weapon uses either the Shooting/Shooting sports skill or Throwing/Throwing sports skills. In the former case, a parry is impossible, unless you are at point blank range (you can also parry for your friend if you are at that range). Also, if your magical girl somehow manages to acquire an automatic gun (or if she has to face a mind controlled SWAT/US Army member with such a gun), a burst gives a +1 bonus to hit, expands 10 rounds, and 1D10 rounds hit, damage is rolled for each round.
4: (Homebrew) Anyone with a skill of 6 in Combat Sports, 8 in Brawl, or 4 in Combat Prowess can deal non lethal melee attacks. The target cannot get lower than 0 Hit points, and as such cannot die, although it can fall into a coma. Anyone with 8 in combat prowess can use non lethal attacks with ranged weapons. All it takes if you meet the requirements is to declare it.
Magical attacks cannot be parried. (Homebrew) Also, if you have 6 ranks in a power, you can use it non lethally (see above)
Standard attack: Make an roll under your power. If you you deal damage depending on your ranks in the power, and how many power points you spend (1 to 3).
Area attack: You attack everything in an area. A high pressure circular water burst, a fireball... You can spend 8, 10, or 12 power points to deal more devastation. You make one power roll against every target. Dodge rolls against area attacks are done at a -2 penalty. With 8 point, you can affect a radius of 5 to 10 meters (your choice), burst center up to 40 meters away. With 10 points, a radius of 8 to 15 meters, burst center up to 60 meters away. With 12 points, a radius of 10 to 20 meters, burst center up to 80 meters away. (Sorry for my use of metric system, but it is the system used by scientists after all... 2 meters are approximatively equal to 5 feet if you want a quick, dirty and approximate conversion.) Making an area attack takes your entire round.
And then, you get combination attacks.
First, take the lower power value of all participant (they do not need to use the same power. Even opposite powers (water/fire) work. This determines the maximal number of magical girls able to make the attack. Then, average the power score of every magical girl. The one whom spend the more points makes the roll with the average value. Then, the defender makes a dodge roll, with a penalty depending on how many magical girls launched a combination attack. (2 to 3: -1. 4 to 5: -2. More than 5: -3). Everyone rolls damage, all damage is added and doubled. Such an attack costs more power points though: it requires one additional power point per attacker for all attacker (for example, 3 attackers means each of them spends 3 more PP for the attack). (BTW, it is possible to make a combined area attack.)
Anytime a high school student is hit in combat, he/she must roll an emotion check to keep control of herself. If you have mastered Brawl, Combat Sports, the courageous trait, or have access to Combat Prowess, your emotions are considered one point lower for this purpose (the four previous conditions are cumulative). Failure means you react badly to the hit, even if it didn't deal damage (panic, rage, freezing...). Also, different conditions can help, like a soothing spell or things like that.
Damage: An ordinary person has 3*Fitness Health Points (HP). Loss of less than one third HP is a light wound. Loss of between one third and two third HP is a serious wound, imposing a -2 penalty to all rolls. Loss of more than two third HP is critical wound. When critically wounded, a character needs to succeed at a Fitness roll or pass out. Then, he suffers a -4 penalty to all rolls. 0 HP is a coma. [homebrew] Negative HP is a dying status. You must roll fitness every minute (with one less second for every negative HP) until you either receive first aid or fail and die. [/homebrew]
Healing: [homebrew] You recover Fitness HP per night of rest. Non magical girl recover 1 HP per night of rest. Someone healing another one during this night's sleep adds his success margin to a first aid roll to this value (half as much in the case of a non magical girl). [/homebrew]
Special case: Magical girls or demons with the Toughness self enhancement power add thrice their toughness to their HP.
Everybody gets it? If you have any question, feel free to ask.
Next and last rule parts: Sickness, tiredness and experience.