18+ Mihitsu no Koi

Yunika, who is very popular at school, receives an invitation from her best friend Risa to study together at Risa's home. Yunika fears that Risa's older boyfriend, who is said to have greatly improved her grades, will also come. When she arrived at Risa's later in the day, Yunika caught Risa and her boyfriend having "fun" with each other.