One day, as Natsuko was washing Mahiro's laundry as usual, Natsuko suddenly noticed the stains and smell on his briefs and realized that Mahiro might have had sexual experience.
How did he masturbate?
What did he use for it?
Who was he thinking of?
Once she became conscious of these things, Natsuko suddenly realized that she was seeing cute Mahiro as a man, and her 10 years of abstinence exploded.
Every morning, after her husband and Mahiro had left, she began to masturbate secretly.

[From Dlsite]