kot

Jevil is parallel to the soul.
He's stuck in a prison, yet he's more free than anyone around him. Similar to how the soul is trapped in a cage, both metaphorically and literally, but is the only person in the narrative with true, unquestionable agency, who's choices matter. While he isn't directly relevant to the plot, his influence is what set things in to motion since he's the one who set King up with the Knight
Spamton is a parallel to Kris. A down on their luck, desperate guy, isolated from the world, receiving orders from a mysterious being on the phone, desperately trying to break free from their fate. This does theoretically make Tenna Noelle in this set up
The Knight and the Old Man are both mentor figures for Kris and Susie. This one is incredibly obvious and doesn't need much analyzing
I posit that the fifth secret boss will therefore be a mentor like figure for Ralsei