While specific plot beats can vary by developer, titles with this name generally center on: The Encounter:
Originally released as an interactive game, it allows players to make choices that influence the progression of the "lessons" and the intimacy of the relationship.
It falls under the "older sister" (Oneesan) and "private tutor" (Katekyou) tropes, which are popular staples in the genre.
Tutor or Temptation? Unpacking ‘Katekyo -Kireina Onesan to Himitsu no Lessons-‘