Reborn: Revenge of the Concubine's Daughter - Chapter 4 - True feelings in the world

Takahiro Nao, a 25-year-old burdened by crushing debt and driven solely by his love for his struggling family, meets a tragic end—until a mysterious Goddess of Benevolence offers him a second chance: reincarnated in another world, and his efforts there will provide for his family back on Earth. Awakening in the body of Naoki von Blackmore, a disgraced “Failed Hero,” Nao is thrust into a realm of sword and magic, monsters, and war, tasked with the impossible mission of defeating the Demon King. With newfound powers, a shadowy past, and the weight of two worlds on his shoulders, he must battle not only relentless enemies but fate itself. Blending emotional depth, thrilling action, moments of humor, and a spark of romance, this gripping isekai adventure asks: how far would you go—and what would you sacrifice—for the people you love?

Dragon 5th is a powerful lord with incredible martial arts, and yet is wasting away from a fatal disease. The only medicine which can cure his sickness lies in the clutches of his venemous ex-wife, Madam Lovesickness, and is guarded by 7 dangerous killers, fugitives of the martial world. To retrieve the antidote, Dragon 5th hires Liu Changjie, a skilled martial artist who loves drinking and women, but has a mysterious past. All is not what it seems in this wuxia heist story.

No family, no power, no inheritance — a thrice-lacking protagonist. Just how will the seed rise up from the mud?

- Description from Novelupdates

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.