Mokoto's mother Ryouko is as hot as even his classmates often say that to you.
The same is true for your close friend Hiroki's mother Aiko.

While talking with Hiroki about their mothers, they reach an agreement that
they will get laid with each other's mother. The sultry summer with
the mothers' sweats and breathes promiscuously scattering begins.

[From DLsite English]