That's right, though it's a little more complicated than an alternate world haha. The main series manga is pretty much just the manga version of the series/movies, but it does have some design nuances I enjoyed. As for spin-off manga, it's sorta hit or miss. Beginning Story is interesting (talks about Mami and Kyouko), didn't care for Oriko, Kazumi was kinda interesting (that's actually different girls), and I haven't read Suzuna or Tart tho Suzuna looks good.
Wow, that's totally not what I have written down. Dunno what happened there. Alright, I need to clone them so I'll get on that.