Overview
Saber is a Servant, the spirit of a hero(or anti-hero) so great they made an impression in the world. In Saber's case, her exploits with the blade were so grand, and her legend so powerful, that she was summoned with a sword-based theme to be bound to someone with great magical energy. Whatever her true past, Saber is a teenage girl with sass and a rebellious streak, but a great amount of pride that both keeps her from admitting she is wrong, and keeps her acting in ways that she believes are proper. As a Saber, she obviously has skill with swords as the name implies, but this class of Servant is also known for having a resistance to magical damage and skill in riding beasts and vehicles. Saber has all of those attributes in spades. Like most Servants, she has an ultimate attack known as a Noble Phantasm, capable of blasting a large area. Quick to anger, slow to forgive, but with a relaxed attitude, her motivations often seem murky.
Perks
Spirit Origin: A creature of mana. Stronger, faster, tougher. Feeds on magic or life energy.
No longer merely a human, Saber is a being of raw magic given flesh. She does bleed and suffer injuries like a human, but her nature as a magical being makes her ridiculously tougher, stronger, and able to move faster than normal humans. She does not need to eat normal food, as long as she has a source of magic, but she can(inefficiently) convert normal food into magical fuel for herself. She can also draw in 'free' magical energy or energy intended to feed magical devices, such as from a mana battery, or feed herself using the life energy of humans. She has no special ability to drain this life, and requires some outside means of tapping into life force to feed on it without simply killing the person and absorbing it from the death caused.
Mana Burst: Bursts of speed and power that explode around Saber. Can briefly walk on air.
Saber has a huge amount of magical energy that she can direct outward or channel through her in brief surges. This gives her phenomenal bursts of speed, or very short but incredible boosts in power, but tends to bleed out into the surrounding area some of the mana in a destructive fashion. For example, shattering ground she's standing on, or damaging any weapon she wields if it isn't of superior or magical make. Her bursts of mana are so concentrated that she can use them as stepping stones in midair, letting her leap about in midair. It isn't true flight, but it allows for some impressive aerial battle and makes up for her preference for melee weapons.
Magic Resistance: Shrug off minor effects, stronger against magical effects.
Saber is highly resistant to many magical effects. This doesn't make her immune to damage, it just helps blunt it, and allows her to shrug off weak magical effects like subtle curses or simple and weak attacks. Saber's magical resistance is quite strong for a Servant, but any dedicated mage capable of challenging her in the field can use magic strong enough to overcome it. It also does not hinder passive effects like that on an enchanted weapon, nor does it help her overcome magical protections like barriers or shield spells. Her resistance only applies to magic used directly upon her.
Servant of the Sword: Uncanny skill with swords. Dodging, parrying bullets, etc.
Like her namesake implies, Saber is excellent at using the sword. Skilled in all types of blades except the most exotic, she is a champion swordmaster, with a style that seems aggressive and unrefined at first. Saber is not an analytical fighter, but one who relies on pure instinct, which makes it difficult for deceptions to work in battle and even allows her to fight hidden or invisible opponents with surprising ability despite the handicap. It even allows her to deflect bullets or other projectiles.
Mystical Knight: Knows chivalry, can ride or drive most normal mounts and vehicles.
With a background in knighthood, Saber knows the typical skills and knowledge associated with knights, such as formations and training and manners of the court. Most especially she is excellent riding just about anything. Horses, giant birds, lizards, motorcycles, cars, planes... if it is a normal mode of conveyance she can ride or drive it at least competently. Highly specialized unique vehicles and very exotic creatures do not apply. Or dragons, even if it's normal for dragons to be ridden in a world. For some reason, no dragons. But Apache helicopters? Fine! Airwolf? No such luck!
Dematerialization: Can turn invisible and immaterial, but not invulnerable.
Since her body is actually a mana construct, Saber can dematerialize into spirit form. This has advantages and disadvantages! It does turn her invisible to most senses, but she still shows up as a distortion on sensitive equipment, and magical senses can easily pick her up. It also makes her immaterial enough to pass through most normal walls, and ignore most mundane damage. Powerful weapons, weapons with magic or spirit behind them, martial arts, and so on can still damage her even in this state, but she cannot effectively fight back without taking the time to materialize, which takes effort and energy. In her immaterial state she is also unable to go through particularly thick walls, nor anything with any magical imbuement, and she is barred by simple spiritual wards even if she could simply walk through them in material form.
Identity Shield: Masks identifying details from senses and magic.
Saber's armor has an innate ability to obscure identifying features, even when she is not wearing it. When in her armor, every detail that could be used to identify her is blurred or has the perception altered, up to and including obscuring voice and figure to hide her true sex, and blurring markings and styles of armor and weapons. This effect even extends to outside her armor, though she cannot hide that she is female when her armor is off. This does not alter memory or keep them from recognizing her as the same person someone encountered before, they will still recognize her as Saber and if she tells someone her true name directly, they will remember it and are free to tell others. Actively removing her helmet when armored dispels this effect until she puts on the helmet again.
Command Spells< Plot >: Limited use magic boosts, enhancements, or teleports usable by Saber's Master.
Saber, when linked to a Master, is bound by a contract symbolized by three command spells appearing as marks on the user's body. While any one of these is intact, she is fed the mana needed to survive without relying on external methods or sources of mana. However, these can be expended permanently to gain a massive boost in magic, healing her or enhancing her abilities. These can boost her abilities much beyond her normal limits, but her contracted Master is the one who decides when to spend them, and the energy must be used toward the 'command' given when using the spell, thus the name. This even allows her to teleport to the location of her Master, even through barriers, or to use abilities that cannot normally be used without Edge or other circumstances.
Complications
Pride: Saber has a need to prove she is the best.
It isn't impossible for Saber to recognize someone as her better, but that will come after a long and hard road. In typical scenarios she is easily egged into competitive behavior within her own skillset, like riding or swordplay, but is less interested in contests that lie outside her interests. Should she end up declaring someone her rival for some reason, she'll even try to outdo them in other things unrelated to her normal skills, often to comedic extremes. Under it all she just wants to prove herself.
Rule of Cool: Practicality is boring. Pick the Awesome approach!
Saber really likes to do things with style. She'll often approach problems in ways that have the most flair, and aren't always the most practical. She won't rely on solutions that obviously won't work at all, but the easiest and straightforward way of doing something is often the most boring, and will only be done reluctantly. She wants to have fun with her tasks! Plus, if there's a chance it will look more impressive if she does it with more flair, she'll do that!
Impulsive: Saber knows strategy and caution. She just doesn't care.
It isn't like Saber is unaware of the benefits of caution. She just can't control her need to do something. She'll plan and think things through if the problem isn't right in front of her, but if the unexpected comes up, she doesn't pause to reassess, she just acts on instinct. Whatever emotion is up at the moment, she acts on it, whether it be anger or jealousy or compassion. She'll rationalize it later.
Against the Grain: Authority is overrated. Saber will rebel and then bel some more!
Authority grates on Saber. She doesn't like being too constrained, or rules abused by those in power, or being restricted from what she thinks is right or fun. This leads to an instinctive distrust of those in charge, and a tendency to go off and do her own thing without telling anyone, or even to question and dig in against orders just to be contrary.