Whatthe: I'm not really sure that our presence would make the story any more credible, though we could at least describe the situation easier. Point is, though, it would be faster, we already know where Yasaka is, and it's not like Nazrin would be any use in a fight :V
Purvis: Like I said earlier, it's faster, and we don't need Nazrin all that much. Though, you do have a good point about getting more information...
So, two options: split up, have Nazrin go to Mokou and we go to Yasaka, or take Nazrin with us to Yasaka.
EDIT: Wait, if Eirin comes to take care of Reimu, then she'll have the information that we'll want. The only other ones that would have credible information would be Tewi, Reisen, and Kaguya, and the two rabbits are probably still recovering from being crazy, and Kaguya's useless.