OK I am going to assume from the translation that, Rin greeted Mystia in the language of the cat which in someway involved a raping. Assertion of dominance maybe?
By group... I hope she doesn't mean the age group...
YojijukugoLit. Four-character familiar phrase (idiom)EirinAnd Orin, please see me after class!*sob sob*Cannoko
Lit: Kyanoko
another "Kanako = Guncannon" (ガンキャノン) jokeOkay everyone, sit down now~!Today, we're learning our native language!Leisure
Touhou MangaOne more!YukarinThese three people are in the ''Four-character mature-lady" group!
'熟語' jukugo: idiom
'熟女' jukujo: mature woman