total affirmation sister is a mistranslation of girlfriend
No it isn't.
"total affirmation" is a bad translation of
全肯定
A better translation would be "very supportive".
So a direct translation of the title
カウンセリングNTR!?隣の全肯定お姉さんを●ックスで……! should be more like:
"NTR through counseling? By sex with the very supportive older girl next door..."
and if you rewrite it to better English and fix the incorrect NTR reference and the weird mapping from "counseling" to "tutoring":
"Counseling sessions with my supportive next door neighbor lead to me cheating on my girlfriend"
Anyway, the trend of stupidly long game names needs to DIAF.