In "There Are Lines", when Sochiro sings this lyric in the second chorus ("You don't load a gun, close your eyes and shoot"), Light doesn't sing the "loading a gun" part as he tries to emulate his father. When one remembers "Hurricane", where Light described using the Death Note as a gun, needing only to aim, Light's intentional omission shows how he wants to shoot with his eyes open, wanting the world to see that Kira is killing the right criminals for his version of justice.
The tune for "Borrowed Time" sounds like "Hurricane", but in a different key. This comparison is meant to highlight how Light's and Misa's determination are one and the same: entirely resolute. While Light is determined to see through his vision of being a benevolent god who wipes out crime, Misa is declaring her firm allegiance to Light, in the face of the authorities that have arrested her.
As the show goes on and Light and L gradually become more and more like each other than they'd care to admit, their duets go from harmonizing/counterpointing off of each other ("Secrets and Lies") to being almost completely in unison ("Playing His Game"), spreading their similarities not just to their personalities but their musical lines.
Light is part of many duets throughout the show, and yet he only ever directly duets with men even though he shares scenes with women during their numbers. Not only does this retain his misogynistic tendencies from the manga/anime, but it also highlights how Light only directly interacts with those who have some use for him - while L is the person he needs to kill and Soichiro is the man he's trying to emulate, Sayu is just a convenient cover and Misa is a tool he can use in his crusade.
