I seriously have no idea what Kanako means in the third panel--is it a reference to one of her spellcards, or something?

^_^ I don't understand either, but it's just so cute in the end LOL!

「影の薄い」means someone who doesn't exude much presence, inconspicuous, etc.

Also re-sized the notes a bit so they don't block as much of the pic. :3

I believe this is a reference to the games. It is believed that the reason Okuu got so power full is because Kanako gave her the power, Okuu remembers her as God that she is.