"I've had enough... Playing God? Justice?! Who gives a damn?! What good is either if the person who took Kimi from me is allowed to walk away?! Screw the system, and screw justice! From here on...I'LL FOLLOW MY OWN JUSTICE!"
Light Yagami (夜神月, Yagami Raito) is the protagonist of the canonical series, Death Note, as well as the secondary protagonist of the fanfiction story, Warning Letter.
After his "reform," and subsequent encounter with Kujo Nobuyuki, he obtained the Persona Dantes, and strove to atone for his previous actions. As a member of the Phantom Thieves, he goes under the name of Kira.
Light is a 17-year old man with brown hair swept to the right, and has brown eyes. As a student, he wore two uniforms; the first consisted of black slacks and a brown blazer with a buttoned-up shirt and red tie, and the second, being his current uniform, has a black blazer with a turtleneck sweater underneath and two chevrons on the collar, and black and red plaid trousers.
As Kira, the entirety of his face is hidden behind a black mask with no facial features, sans they eyeholes, and has four diagonal stripes around the eyes as if making a make-up mask. The strips are of different colors, such as green, red yellow, and blue. His attire consists of a white coat with a fur lining at the collar, an dress shirt with the first few buttons undone to reveal an ascot bearing an insignia of an inverted cross. He wears black slacks, and combat boots.
Prior to obtaining the Death Note, Light was a diligent high-school student who took his studies seriously, though this stemmed from the fact that he wanted to become a police officer so he could bring the man who murdered his childhood friend to justice. He was shown to greatly distaste the current justice system, even calling a world where everything was put on endless repeat 'rotting.' When he obtained the Death Note, his personality took a darker turn, and while he maintained a diligent and hard-working and honest appearance, he had developed something of a 'god complex,' now having the power to kill virtually anyone, so long as he knew what they looked like, and their name. He wished to make a world where people who worked hard, were kind, and were honest could live in peace without scum interfering with their lives, though he believed that anyone who went against him was also evil. This was shown when he murdered Lind L. Tailor, who claimed his actions were evil.
His Shadow showed was more or less an embodiment of this facet of Light's, which became known to the public as Kira. Shadow Light was one who detested any act of violence or wrong done to another, and viewed the instigator as 'evil.' As a result, he considered the Phantom Thieves to be evil for their actions in defying him, the "God of a New World." However, he himself recognized the Phantom Thieves of Hearts to be following their own code, and called for an alliance. While he displayed a calm, regal yet menacing demeanor, he was highly conceited and arrogant. This, however, began to break down when the Phantom Thieves started to overwhelm him, becoming angry and frustrated, claiming that any who defied him would be cursed and punished severely for this transgression.
Following having his Treasure stolen, Light has become remorseful of his actions. Unlike the previous targets of the Phantom Thieves, he has not confessed to the police, primarily because of Sayu. He suffers from slight trauma, often having nightmares of the people he's murdered with the Death Note. He has also started to fall behind in school because of this, and receives less sleep than normal, resulting in his family becoming worried for him. However, after encountering with Kujo Nobuyuki, and remembering his face as the man who killed his childhood friend, Light returned to his previous self, but discarded the notion of being 'God,' as not even a God could revive the dead. Recognizing his own actions as self satisfaction, he resolved to instead take matters into his own hands, and follow his own justice, thus leading to the awakening of his Persona, Dantes.
Since joining the Phantom Thieves of Hearts, Light has developed a more serious attitude. Like the others, he takes his newfound profession seriously, and states that he wants to atone for his actions, no matter how long it takes him. Light has also become more playful, often teasing Haru about her crush on Miura.
Light, even from a young age, was a brilliant child, having scored the highest in his fourth grade class, and was very well-mannered, earning him a large social circle. His grandfather was also a prestigous police officer, and Light greatly respected him, saying that he would be like him one day. This led to him often seeking advice, and training in some sense, to become a member of law enforcement, though his father opposed this initially. However, when Light was twelve, his grandfather died due to a heart attack, which left Light in a state of depression, and barely spoke with his parents at all since then. It wasn't until he was fifteen that he got over it when he met Kimi Mako, who became his emotional crutch. By that point, Light had seemingly forgot about his desire to become a police officer.
A year later, tragedy struck. Kimi was hit by an oncoming car. The incident had nearly left her all but paralyzed, and despite who was at fault, the driver shouted and denied the accusations, saying that she was the one at fault. Light was furious, and nearly attacked him before being pulled away by the authorities. Kimi spent several months in the hospital in Intensive Care, with Light visiting her every day. Despite the assurances of the doctors, Kimi died several days later, leaving Light once again in a state of depression, and skipped school for almost a year. He became extremely bitter when he learned from his father that the man who hit Kimi was actually a regular thug who was thrown into jail on various occasions, and yet somehow managed to avoid being tossed back into a cell.
When he learned this, Light became furious, and soon began attending school, rekindling his desire to become a detective, so that he could put scum like the one who killed Kimi behind bars where they belong.