It's criminal these two never met in any official Touhou work! The only screen time they shared was on the character select screen from Touhou 5 Mystic Square! o.o

Dialogue!

Both: "You're also a final boss?! BESTIE!!"
Mima: "You missed Touhou 3!"
Yuuka: "I was sleeping♥"

機械翻訳
二人「あなたもラスボス？！ 親友！！」
魅魔「東方3見逃したのね！」
幽香「寝てた♥」