forreal tho the whole Point of durarara as a work of art is thhat nobody is wholly good (obviously) OR wholly bad, people are complicated and their relationships with each other and the world are complicated as well
izaya as the closest thing to an antagonist the series has, ALSO serves as mikado's foil- he's the bad end to mikado's story, explicitly becoming that way because he had no true friends- shinra only cared about celty and his parents were never around and thats kind of all he had. he was a young boy with clear mental problems, to the point where his father instilled that people love into him in order to prevent a worse outcome and help him be more normal. the way this is framed, as a young boy exhibiting a concerning disconnect from other people to a point where it scares a usually neglectful father into acting- is very reminiscent of media depictions (and real life examples) of parents worrying that their child is a sociopath. this could very well have been intentional, and narita EXPLICITLY makes a POINT to state that izaya is the way that he is because he has a fragile heart- any sort of genuine effection and a betrayal of it could shatter him. i really dont think the takeaway here was "lolllll hes suchhh a loser" OR "omggg hes so scary hes iredeemable." it's another piece of the central theme that humans are nuanced and messy and conplicated and oftentimes in very unglamorous ways that make them unsympathetic to most people. durarara AS A SHOW is about shining a light onto these people and inviting the viewer to sympathize with them, and if someone doesnt get that and is just disgusted by most of the characters then durarara is not the show for them
also vis a vis izaya and mikado being foils- the reason mikado got a happy ending was because of his friends- because of the connections he has with other people. izaya did not have those connections, hence his own instability drove him farther and farther down into a death spiral that culminated in his CRIPPLING, a major loss of freedom from someone who valued it so much, and i'm saying that as a disabled person
anyway yeah