Watashi ga 15-sai dewa Nakunatte mo.

Iwashita, a middle-aged salaryman, is living a modest but repressed life, shunned by his daughter and nagged by his wife. Until one day he ran into a girl named Chyna. She offered Iwashita a meal for 20,000 yen - an invitation to become a daddy. This is the beginning of a painful but dazzling story of a 15-year-old girl searching for self-worth and a 40-year-old middle-aged man struggling between reason and desire.
(Source: Funguild, translated)