Not to pretend that Death Note is deep but Death Note The Musical 2015 Urai Kenji with english subtitles is deep actually and I love their thesis on what Death Note is about
Like every adaptation is also inherently a thesis on the source material since the question "how can we express this in a different medium" cannot be answered without knowing what the original material is supposed to express in the first place. Or at least what it should express depending on how much they change it, but Death Note The Musical is a very faithful adaptation and follows the original almost step by step except for the fact that it ends sooner, has songs, and cuts a few parts off to fit the limited time, so I'm gonna go with the first one
And their thesis is that Death Note is about love. Specifically, all-consuming love, in its ugliest and in its most beautiful. It's not about genius deductions or the lawlight pissing contest or even about the most obvious moral and political discussion on criminality and punishment (thank god, because Death Note doesn't do that right at all). It's about a web of profound, deep, all-consuming loves. Misa's love for Light. Rem's love for Misa. Light and L's weird love for each other (which is pretty much canon in the musical, see: tennis duet). Love at its most unhealthy, selfish, and self-denying (lawlight) versus at its most selfless, beautiful, and fulfilling (remisa)
The driving force of the entire plot is love - except for Ryuk, who is driven simply by boredom, and is always shown obviously out of place in literally every scene. Light and L deny it, and love in a selfish way - they want to consume each other, become one, annihilate the other. Misa and Rem love selflessly - they want to make their loved one happy. And that is the ultimate difference between them, that defines their trajectories and their end
In a canon where the protagonist calls himself a god, the one to have the heavy religious imagery place unto them is Misa. Specifically, Misa after sacrificing everything for love, Misa after singing that the value of a life is defined by how much you love, that life is fleeting but love is what stays. Misa is ascended in that moment, so much so that a real goddess worships her at her feet, happily choosing to give her own life for Misa. And that proves Misa right, because in that moment, love does kill death - metaphorically and literally
(Meanwhile, the protagonist who sings about sacrifice dies pointlessly and sadly, after killing his own love. And he does so, again, literally and metaphorically. Literally because he killed the one he was in love with, metaphorically because he chose violence and greed and abandoned and deceived the ones he loved the most - Sayu and Soichiro - before it all. So when I say love, I'm not talking only about romantic love, even though I know that's the form of love Misa is singing about)
And that makes Death Note a proper tragedy and at the same time not at all like one, because Rem is happy, and so is Misa, despite having nothing left. It is L and Light, who wanted everything, who die unhappy and empty. So it's also about greed, but that greed is also shown through the way they love - consuming in the worst way, meaning taking the other and annihilating them into you, consuming them, taking them for yourself. It's an interesting take in how love as deep as Rem's for Misa and Misa's for Light can be ugly and twisted, and not at all romantic
And it's not at all the take I expected them to have from Death Note but damn I'm glad it was
