Selects default stylesheet for people using screen readers.
Screen readers don't always use the stylesheets designed for screen readers. That makes it difficult for blind people (who frequently rely on screen readers) to use the internet.
I know, right? Hopefully this helps people who have to use screen readers to surf the web.
TL;DR: This makes the web easier to use for people who are blind or have low vision.
Batou is the name of a character from Ghost in the Shell, who uses bionic eyes to see.