Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 5 - 5-3. Black Mist

Life used to be so simple,

Full of false hope and endless beliefs in one’s ability in wooing that beautiful girl.

But in a single instant,

Everything as you knew it, plummeted faster than a spoken rejection.

What is real and false can’t be determined,

As the world slowly falls into the maws of the apocalypse.

How will our simple friend respond to the call; the summons?

No matter what he chooses,

Chaos SHALL Reign!

- Description from Novelupdates

Going for a swim, she ends up in an ancient wild Beast World and ends up being brought home by a handsome wolf.

I had been abroad to do medical volunteer work, when I was swept up in a civil war. I was killed by a rebel soldier, while taking a bullet for a patient. But when I finally woke up, I had become a child?!?And in front of me stood a destroyed carriage and a group of oddly dressed people, who were unconscious!“It’s just like a Murim world.”As I hurry to perform first aid in an attempt to save even one person, I realize that this world is that of [The Supreme Demon King], a Wuxia novel I’ve enjoyed reading.After meeting the rescue team of the ‘Three Great Doctors’, I found out that one of the person I saved was the protagonist of this novel, the future Demon King ‘Yeo Haryun’!“Hey, since I’m indebted to you for saving me, call me ‘hyung’.”For saving his life, I become sworn brothers with the future Demon King, and the White Dragon Godly Doctor, one of the most knowledgeable people around, recognized my potential and took me in as his disciple. This is the story of how I became the greatest physician in Gangho!

The old man pointed to the flower-like woman and said, “Call her mother from now on.” He then pointed to a flower-bud-like girl and said, “This is your sister.”

My younger sister was not cute.

She was arrogant, taciturn and weird, but she knew how to please our parents.

She was two-faced and deceitful, but it seemed like she only treated me that way.

I cared for her, tried to please her as much as I can, but she still disliked me.

Until one day, I found out her secret, our relationship began to get a little bit weird…

- Description from Novelupdates