When examining the themes of Death Note we as a fandom have a lot of input. Death Note is the perfect slate for a variety of interpretations because Ohba himself didn’t have much in mind outside his desire to entertain his readership. When interviewed he said that he saw a magazine article about the themes of the series he stated that it was “too difficult for me to understand” and the creation of the “deep philosophical themes” of Death Note were a by-product of their desire to entertain, not the other way around.
He’s even on record as saying “some people may have been taking the series too seriously”! (Which in writing this article I’m probably falling into the category of). He was pressed about this topic and did eventually say “no human has the right to pass judgement on another’s actions. No one should play God”; but this seems to be retrospective analysis rather than something he had in mind while writing the series.
Nevertheless, whether Ohba intended to or not his series raises many valid ideas and paves way for multiple readings; not just the one I’m about to offer. The risk in approaching Death Note is to view it with too strong a Western perspective when characters like Soichiro Yagami are so clearly eastern. Nevertheless, it’s through this lens I will (partially) view it because of my greater familiarity with Western philosophy.
The three main ideologies characters could be argued to have in the series are Utilitarianism, Confucianism (with a touch of Kantianism) and Nihilism. We'll start this month with the middle one.
Death Note's Confucian Soichiro Yagami (and Kant)
Soichiro values his family above all other things, and his duty as a police officer next. He was the first to agree to stay on with L after the police force stopped investigating the Kira case, and his guilt in saving his daughter lead him to accept the Shinigami eyes and ultimately die for his cause. He risks his life numerous times during the Kira investigation and his passion for justice makes him an incredible workaholic (his family often had to deliver clothes to him because he worked such long hours, this caused Light to meet Naomi while he was delivering them to him; too her eternal misfortune).
Ohba has stated that Soichiro Yagami is the only “good” person in Death Note.
Despite his dedication to catch Kira, he has his limits of what he perceives as morally permissible to do so and he certainly doesn’t espouse the idea “that the ends justify the means”. This objection is revealed multiple times throughout the investigation; most notably when L wishes to allow criminals mentioned by Yotsuba to die in order to incriminate the organisation. Soichiro opposes on the grounds that “even if they are criminals” it’s unethical to allow them to die even if it is to solve the case. To make this clear, they arguably stand to gain more by allowing these criminals to die (and to be fair, we aren’t talking about purse snatchers here in most cases) since if they can apprehend the Yotsuba Group, more people will be saved from Kira.
Looking it at it from a more Kantian perspective all humans have an intrinsic value, and can never be a means to an end because their intelligence and sentience makes them an end in of themselves meaning things such as murder and lying (which Light does with impunity) never acceptable.
The song sung by Soichiro in Death Note the Musical - Honour Bound and Bound by Honesty - has a distinctly Eastern feeling to it; enhancing his Confucian and Japanese associations.
Other versions of Death Note enhance this very Japanese perspective further. In the Death Note drama, Soichiro Yagami commits suicide with the Death Note after uncovering his son’s identity as Kira. This harkens back to the honour killings that were once common in Japan; most infamously with Kamikaze pilots. Since Soichiro Yagami cannot bring himself to kill his son (that would be a violation of his duty to his family) he kills himself since he failed in his duty to raise a morally upright son.