Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 4 - 4-7. Satou's Secret

With the Goddess’ blessing, he became a 『Divine Knight』 and founded an Empire.
As time passed, he grows older, and by the time the heavens called for him to come, the Goddess showed before him, asking for his last wish.

He wished to be reincarnated in the future.
He dedicated all his life for his people, he had no time to master his own arts.
This time, he wishes to live for himself, forging his body to the utmost limit.

The Goddess complied with his wish.
In the far future, the King shall reincarnate as the 『daughter』 of a renowned Knight family.
And, under some circumstances, she is labeled as a failure of a Knight, however——

「How convenient. I can stand on the foremost line without needing any rank. No better training than actual combat!」

Thus, the legend of the world’s strongest, most beautiful Knight Disciple (♀) has begun—

“Obtaining the topmost degree of talent in sword arts in the world requires giving up 72 years of lifespan, which leaves you with only five more years of your life. At the same time, you will never be able to feel love, kinship, and friendship, and you’ll end up leading a lonely life until your death, unable to procreate, or to have any descendants.

“From now onwards, everything related to happiness in the human world shall no longer be of your concern. Are you willing to accept this?”

“Hahahaha, I’m already alone bereft of all support, my hopes dashed to pieces, shouldering only absolutely irreconcilable grudge and hatred, why would I disagree? Why would I not want it? I couldn’t ask for anything better!!”

His sword sweeps across the Divine Continent for seven days and nights, moving 90,000 miles through the starry skies, unhindered.

He slays saints and buddhas in Heaven, slaughters demons and devils in Hell, sweeping away all the grievances in his heart.

With a marriage contract forcefully done, he married her, and all she could do was comply, and resent him deeply for that and for all the following misunderstandings they faced, and she understood too late she loved him.

But after a life of misfortunes, she’s reborn to the very beginning, the day he told her they were married, and she was determined to cherish him in her second life!

Lin Mu Mu’s life goal is to : grow flowers and plants, and take care of Yun Ting.

Yun Ting’s life principles are : Love Lin Mumu, Love Lin Mumu, Love Lin Mumu!

- Description from Novelupdates

When she was eighteen, she was forced to take her sister's place and married him, who was disabled in both legs and impotent therefore.Despite all this, she has accompanied him through the darkest period of his life.However, two years of marriage and companionship still couldn't compare to the return of her sister.In order to treat her sister's illness, he even cruelly forced her onto the operating table, disregarding her pregnancy.His cold-bloodedness and ruthlessness left her heartbroken. After leaving the weak and sickly second child with him, she disappeared with the other two children.It wasn't until he completely lost her that he realized he had already fallen deeply in love with her.......Five years later, she returned with mini versions of their child.Looking at the adorable child who seemed like a spitting image of his son, his face turned pale.“Why do you look exactly the same?”The little one replied, “Biologically, only identical twins look exactly the same.”“?...”Did she give birth to twins?He angrily cornered her against the wall and asked, “So, you had twins back then?”She chuckled awkwardly, “If I say it was triplets, would you kill me?”