Death Note is full of symbolism; from the Catholic Christian overtones (apples, Divine Rule, and the Shinigami Realm) to literary masterpieces (Macbeth, Julius Caesar, and Sherlock Holmes), Death Note has become one of the few anime to have extremely deep roots in both Western and Japanese cultures.
The most obvious symbols used in the series are apples and the conflicting ideals of justice between Kira and his opposition.
Apples are symbols incorporating a variety of meanings within a variety of contexts. They can mean knowledge, wisdom, luxury, joy, and/or death. In Greek mythology, apples appear repeatedly: the goddess Hera received an apple as a gift of fertility upon her engagement to Zeus, King of all Deities. Apples, in regards to the Garden of Eden, were the first symbol of temptation and Original Sin. In secular ideology, apples function as a symbol for totality, as in the "cosmos" or "universe," due to their nearly perfect spherical shape.
What can be applicable to the series is how the apple represents temptation and the Original Sin, considering the first opening of the anime is alluding the apple to the Death Note, which is similar to that version of the apple in that regard.
However, in Death Note 13: How to Read, Tsugumi Ohba states that there was no underlying reason for his choice of apples. He is quoted as saying that he liked the way the red apples contrast with Ryuk's dark appearance.
Justice has many underlying meanings. To understand the concept completely, we must first examine the origin of law begun by Hammurabi of Babylon (1795 BCE) as well as the Bible (Old Testament: 450 BCE, New Testament: 45-140 CE). In addition, we must also analyze the various goddesses of Justice: Ma'At (Egypt), Themis (Greek), and Justitia (Roman).
The first written code of laws was written by Hammurabi of Babylon, whose name translates to "the kinsman that heals." He is the first (known) historical creator of what we call justice, or law. His code of laws are still in practice by people all over the world to this very day, whether they know it or not. Without Hammurabi, laws and morality would probably not exist as they do today. That is how important his work was to the entire planet.
The Bible came along over a millennium (1000 years) after the time of Hammurabi and Babylon. Beginning with the Old Testament (a.k.a. the Talmud, Torah, or Talkh). In circa 450 BCE, Moses' "10 Commandments" became the earliest concept of morality, not law. If one were to give a poll asking most of humanity: "What is right and what is wrong?," and the majority will generally tell you something along the lines of what is stated in the "10 Commandments."
Many of the details beyond the "10 Commandments" were vastly expanded upon, as well as changed by, Jesus Christ of Nazareth. His teachings discarded many Jewish notions of law and justice, even though he was once a Jew himself. For instance, in the Old Testament: "An eye for an eye, a tooth for a tooth." In the New Testament, Jesus' mantra is "Turn the other cheek." This is a vast contrast to the old ways, which were beliefs based almost entirely in Judaism.
L also mentions that Kira may have a "childish" concept of right and wrong.
Many other contributions have been made since then, including Rome's creation of the original justice system, the Confucian belief system and philosophy, as well as America and its ideal-driven culture.
The entire story line of Death Note is similar to Shakespeare's Julius Caesar. Light Yagami can be compared to Marcus Brutus, Misa Amane to Cassius (often speculated that Cassius was gay), L to Julius Caesar, and Mello and Near to Mark Antony and Octavius Caesar. Just as Caesar's ghost appears to Brutus before the decisive battle, an image of L returns to Light after the time-skip during a pondering moment of Light on Mello and Near. (However, the motives are different. Brutus perceived Caesar as a threat and loved both him and Rome enough to slay.)
Just before Light has Rem kill L, L receives prophecies of his death in the forms of images and dreams (more than once). In the same way, Jesus prophesied (more than once) that He would be betrayed and killed. Also, Jesus washes the feet of His disciples, including Judas—just before the latter betrayed Him. In the same way, L washes Light's feet after their conversation in the rain on lying (although this scene was only in the anime, not the original manga).
Doves and crowsEdit
In both the first opening and ending from the anime, many crows appear near Light, and Ryuk is shown along with some crows on top of a tree. Ryuk's wings resemble that of a crow's, the bird being a symbol for both bad luck and death, just as Ryuk told Light that a Shinigami only brings disgrace and bad luck to the human to whom their Death Note belongs.
In the first ending, before the chorus, Light is shown in front of a blue background, surrounded by white doves, all of which fly away. The picture is then horizontally flipped, and many crows surround Light in a red background. In Christianity, the Holy Spirit is symbolized as a dove and appears as one during Jesus' baptism. They are also a common symbol for peace.
Doves abandoning Light to be replaced by crows could be linked to their respective symbols.
The fact that Ryuk is shown along with the crows in the first ending can also be related to the fact that crows usually gather next to an animal or person about to die, only waiting for that person or animal's time to come, just as Ryuk sits around and waits, during almost the entire story, to see when Light's time of dying will come.