Swaple Medicine by zerowan - Adult Sex Game

Tachibana Miku is Takumi's fiancée. Both of them work in the pharmaceutical department.
As well as:
- Takumi's brother who was in love with Tachibana Miku. After she preferred her brother to him, he harbored a grudge...;
- A school friend and classmate of Tachibana Miku - Reiko Kishiragi. She fell in love with Tachibana's brother Miku, Takumi, at school.

While working on a new drug, they noticed a hidden effect! The new drugs had the property of increasing sexual desire.
The heroes took advantage of them and as a result, the couples changed their sexual preferences.

P.S. Passwords will be needed to "scroll" the plot history