The Tobu line has a pass for Nikko. It leaves from Asakusa station and has, depending on your needs, passes to different spots. I'd check out the site below and see if it's worth it for you. I learned that from
Free Worldwide Travel Guides - Wikitravel. If you type Nikko, some interesting info pops up with some worthy options.
TOBU LINE GUIDE | Asakusa Kawagoe Nikko | Japan