The protagonist Toa, and her childhood friend Miu
would do everything together. They were just like family.
To Toa, that was such bliss that she wished it would last forever.

However, as time passed and they changed both physically and mentally,
their circumstances and the reactions of others changed in tow.

On top of that, something happened to a "part" of Toa's body,
and due to a certain event, Miu became aware of that change.

He shows concern about it of course, but...

Toa thought her cute childhood friend was harmless... but looks can be deceiving.
It turns out that he had been sexually training her while he was unconscious...
A sexually naive mind, experiences consecutive orgasms from her sexually primed body.