ママのおっぱい ～俺の童貞ミルクが搾り取られた件～

And the other one. A lady who helped take care of something around the house until his father's second marriage.
She is his father's younger sister, making her Makoto's aunt, Kaho.

While helping these two beautiful older women, he never experienced loneliness and grown up quickly, but...
He failed his university exams, and is currently on his second tries.

And the cause of all of it--"boobs".

Ayame and Kaho, he can't get these two beautiful older women out of his mind, so much so he can't focus on his studies. Especially those beautiful breasts; if he reached for them, he could feel them anytime.

Worrying endlessly about that, one day he was helping around the store, when unexpectedly Kaho teased him about the size of his genitalia, making him lose self-confidence in his manliness.

Unable to concentrate on his studies, he worries about becoming impotent.
Seeing him like that, Ayame helps him, even while know what she is doing is immoral.

"It's okay, your stepmother will teach you every part of a 'woman', and make you a 'man'--"

[Translated from Getchu]