Why does Death Note look so realistic?

Start with the clothes. Obata has said he put a lot of effort into Light's wardrobe and, finding it hard to imagine what a brilliant person would wear, worked from fashion magazines. The result is a wardrobe of fitted formal shirts, with jeans deliberately avoided, because Light is a smart, formal guy. When the story reached Light's memory loss at chapter 35, Obata had to go back and draw him exactly as he had in chapter 1, and felt how much his line had simplified since.

L was engineered as Light's opposite. Obata asked Ohba whether L could be unattractive; Ohba's thumbnails showed a plain face with no bags under the eyes. From chapter 11, when L appears in person, the two creators agreed to contrast him with Light. Obata added the black bags after his editor asked for a face that looks cool from any angle, citing the appeal of the same feature on Devilman's Akira Fudou, and built in a dead eyes concept: all-black eyes and almost no eyebrows. His outfit is a plain white long-sleeved shirt and jeans, because L does not put thought into choosing clothes.

The same reference habit runs through the rest of the cast. Misa's Gothic Lolita look was chosen to carry the gothic imagery of the shinigami world, and Obata worked through Gothic Lolita magazines to draw her, before restyling her as a popular actress later in the series. For Rem, his starting points were fashion designers' impossible silhouettes and Medusa's snakes.