This is the R18 version which includes adult sex scenes!

"Bear my child instead of your sister..." I used to think there was no love in marriage... Until I met a fierce and passionate soldier!

Despite being the daughter of a viscount, Asako is rejected by high society and treated as a nuisance by her parents. When a marriage proposal arrives suddenly for Asako's younger sister from none other than Captain Kido, a soldier known for his coldness, she doesn't hesitate for a moment. To protect her precious younger sister, Asako volunteers as... a substitute bride!

A Ruthless Soldier X the Lonely Daughter of a Noble - A passionate romance in the Taisho era, sparked from an unexpected marriage!