Hitozuma Onee-san to Tsundere Osananajimi no Haranda Kankei

Kouki has two old friends, Yukiko and Rio. When he was a university student, Yukiko got married and left the town.... However, she is back to the town now. Kouki still loves Yukiko and his pent-up sexual desire explodes. Rio, who loves Kouki, notices it and approaches him in various ways....