Black Star is the son of "White Star" of the "Star Clan". Each member of the clan is branded with a star tattoo somewhere on their body. For Black Star, his tattoo is found on his right arm, just beneath his shoulder.
The Star Clan, otherwise known as the Hoshizoku, were notorious assassins, who would do nearly anything for money. However, 13 years prior to the events of Soul Eater, they were completely wiped out by the Death Weapon Meister Academy (well, all but one).
There was, however, one surviving member. Who was, of course, Black Star. He was taken in, and raised in the Death Weapon Meister Academy. He bares no grudge against the academy, and has gone so far as to state "My old man, and mom were wretches too... so they got killed... and that's all there is to it...". Over and above this, he states if it were not for shibusen (the school), he would not have received the public attention he gets now, and (in his opinion) deserves.
Black Star's training is rigorous and brutal. When studying for the Shibusen exams, he did five hundred one handed, hand-stand push-ups when he answered the first question wrong, and then went on to do one thousand crunches after getting the next question wrong. He is often seen exercising to this degree.
He's also been seen training with Doctor Franken Stein, and fighting on par with him in unarmed combat. Later in the manga, he is even shown replicating Stein's "Soul Menace" technique.
He's also trained with Tsubaki in the art of assassination, and has been stated, and shown as a master assassin. Over and above this, Sid Barett has described Black Star as a "heaven sent warrior" during his final battle with Mifune.
Black Star's Techniques and Stats
Black Star studies the art of assassination. In his first appearance, he seems to have issues with the aspects of stealth, as he often shouts his name upon arrival to notify everyone he is there. However, when he is serious about a situation, he can often take advantage of his opponents blind spots. This is shown in two out of his three fights with Mifune, as well as against Stein, Tsubaki's brother, and Sid Barret.
Adaptable Fighting Style
In several of his fights, Black Star has shown the ability to come up with new fighting styles on the fly. In his fight against Tsubaki's brother (due to the slippery footing), he fought heavily through jumping and taking the high ground, and once his opponent was coaxed into the air, he stated "Mid-Air Attacks are from my era!" and finished off his opponent quickly. In his final fight against Mifune, he created an entirely new sword fighting style on the fly in order to counter Mifune's fighting style.
Black Star's "Big Wave"
Big Wave is Black Star's signature move. It consists of two consecutive attacks. The first of which stuns and paralyzes the opponent in place by jabbing his elbow into their spine. The second is a double palm striking, pushing his incredible soul wavelength into his opponent's, either killing, maiming, or stunning them. This attack makes several appearances throughout the manga, getting gradually more and more powerful.
Soul Menace is actually Doctor Franken Stein's signature move. When training with one another, Black Star learned to replicate this technique. It does not appear to be as strong as "Big Wave", but because it only requires a single palm strike, it is performed far more often. Presumably because it is a much simpler technique.
Planet Destruction Cannon
This is Black Star's ultimate technique, and is only used once in the manga as of yet. It was performed against Mifune in their final battle, and was capable of knocking him back and stunning him for awhile. The effects may not have seemed very impressive, but Mifune is trained against these sorts of attacks. For it to do any sort of damage to him after he had prepared against these sorts of attacks, and with him no longer holding back, is a pretty remarkable feat.
Techniques via Tsubaki
Weapon ArsenalTsubaki can naturally assume a wide number of weapons. So far, she has been observed turning into the following: katana, ninja sword, speed boost (amplifying his speed), smoke bomb, a decoy, chain sickles, and a shuriken.
This creates a protective barrier in front of Black Star, capable of stopping powerful attacks that hit the barrier. It can be created mid-air, and is (as the name implies) in the shape of a giant star. The diameter of the star looks to be about fifteen feet.
Very similar to "Shield Star". Any opponent that enters the area of the Trap Star can cause it to instantly close. When this happens, it traps whomever is inside of it in Tsubaki's chains.
This is a special technique, where Tsubaki becomes pure shadow. It chains an opponent in one or multiple areas, and then performs a brutal cutting technique. Even when every attack was incapable of even harming their opponent, this attack was capable of severing both his hands simultaneously (Mosquito was the opponent)
First Form - Chain of Blackness
This form is a powerful offensive/defensive type. It surrounds Black Star in a circle of shadow chains, which serve to parry and protect him from incoming attacks. However, this form also has two sword sized blades in which Black Star can hold onto, allowing him to dual wield, parry, and attack much the way he would with a normal sword. Over and above this, he can throw these weapons, and manipulate the trajectory of the attack mid-flight via the shadow chains. This allows him superiority in mid, and short ranged combat.
Second Form - Moon Night Leaf
Second form contains a lot of special maneuvers within it, giving him extreme amounts of versatility. First off, as a shuriken, it can be thrown long distances, and it can cut through almost any substance. The second benefit comes from his ability to wear it, by inserting his hand through the center hole. While it is being worn, it creates a black gauntlet around his hand, which so far has not been damaged. It also spins constantly around his arm, granting him incredible cutting power, and can be used as a shield to block attacks. The final benefit, is once his hand is inside it, he can unleash powerful energy blasts from his hand. It also seems to produce wind while spinning, dissipating smoke, kicking up dust, and etc.
Third Form - Absolute Shadow
Absolute Shadow serves to increase Black Star's speed tremendously, as well as give him some form of shadow manipulation. He is said to move at the speed of shadow, and he leaves behind afterimages whilst attacking. But unlike normal afterimages, they do have mass, and can hit opponents. Realistically, they are closer to Shadow Clones than afterimages, but it is revealed they are a byproduct of his speed.
Fourth Form - Dark Limb
This attack is first used against Mifune, and is used seamlessly from his Absolute Shadow technique. The effect of this technique is similar to Tsubaki's "decoy" technique, in that she adopts his voice and appearance. However, unlike a regular decoy, her physical stats are also increased to similar level to Black Star's. That, combined with her incredible training and technique, makes her a formidable opponent to go against. Over and above this, it serves as a distraction, for while the opponent is occupied fighting Tsubaki as Black Star, Black Star is usually capable of setting himself up for an attack. This allows Black Star to set himself up for Big Wave, Soul Menace, Planetary Destruction, or even just a bombardment of attacks.
Zero Form - Masamune
Masamune form creates a katana, and also brings Black Star's shadow to life. The Shadow rises up to him, and acts almost as a second appendage. It flows to his will, and can be used to attack, support his weight, slingshot him long distances, parry attacks, and so much more. This form is considered Black Star's ultimate technique. Over and above this, Tsubaki can control the weight of the blade, making it lighter or heavier, depending on Black Star's will. The Masamune can also be sheathed into the shadow, and retrieved at will.
Capable of holding a giant off the ground with only one hand, holding onto a 20 square foot chunk of stone and throwing, and sending opponents flying through structures are only a few of Black Star's feats in this department. He's also the only character as of yet to cut through and pierce Black Blood attacks.
In his first appearance, he was capable of dodging a hail of machine gun fire from dozens of opponents without being hit. He's dodged and parried sonic attacks (at least Mach 1) coming from every direction while yawning and giving zero effort. He has been shown blocking, deflecting, and even catching light beams with his bare hands (doing several of them simultaneously actually) and throwing them back at his opponents.
At his base form, without Tsubaki, he was timed at running a one hundred meter dash in about five seconds (45 miles per hour), however, this is an outdated feat. With Tsubaki's enhancements, he can move at the speed of shadow. Which is, at the very least, massively hypersonic.
Black Star's durability is unparalleled in Soul Eater. He was capable of swalling an attack capable of creating a giant mushroom cloud without so much as losing consciousness. He's stood up to grenade level attacks without so much as a scratch on his person, and was able to take hits from Black Blood attacks (which is a nearly indestructible material).
Black Star has a big personality. He's loud, always wants to be the center of attention, cannot stand being ignored, and views himself as stronger than the gods themselves. However, he also takes pride in his friendships, and will go out of his way to protect them.
He's also a grade A pervert. On several occasions he has been found peeping in on the girls while they are naked, while reciting his rules of peeping. Despite being a master of stealth, he often find himself getting caught.