Keisuke coveted his older brother's wife. One night at dinner his brother revealed that he was infertile.
I can't father a child, said the drunken brother through slurred speech, we even went to a clinic.

Then he passed out. Beautiful wife Aya tidied up.
Keisuke saw an opportunity. Emboldened with booze he followed her into the kitchen,
and ravished his brother's wife then and there.

The next day Keisuke felt regret too powerful to face them.
He steered clear of his brother's house.
But when he got home, Aya was waiting.

"Keisuke-kun... make a baby inside me......!"

[From DLsite English]