Shinigami in the Ninja World - What If 12: Danzo’s Death, Eternal Mangekyō Sharingan

She, a 21st century mercenary queen, had crossed over into a tragically betrayed body of a waste. Waste? She will show them what it means to be a waste! Betrayed? With the Ancient Manual in her hands, she will astonish all the despicable men and cheap women!

Qiao Zhenzhen spent a lifetime, only to later realise that she was the true heroine of a novel. According to the original plot, her life was supposed to be smooth sailing and blissful. But the envious transmigrated second female lead played her cards step by step, and took everything away from her!

After experiencing the divorce of her parents, and miserably failing the college entrance examination, she gets kidnapped along with her little follower of a male lead, Chi Shen. In the end, she came out as the only survivor.

Everyone believed that this was a blessing in disguise, not only was her life saved, but the pervert stalking her for the last three years was also gone! A freak like Chi Shen, who had a weird and eccentric personality, always stank of fish and grease, was better off dead. Everyone said that she ought to be grateful, but none of them knew he died protecting her.
Before he took his last breath, his dying words were-

“Don’t be afraid of me.”

That sentence, mixed with the smell of greasy fish and blood, flashed in her dreams every night for the next decade.

Reborn back into the senior year of her highschool, she walked to the youth in the corner, and in front of everyone’s eyes-

“Don’t hideaway in the dark if you don’t want me to be afraid of you.” The youth pursed his lips, his pale face steadily losing color.

Qiao Zhenzhen smiled: Be nice to me, and I shall allow you to stalk~

- Description from Novelupdates

At the end of the world, a legendary hero gave his life to save a dear friend, only to be reborn as a four-year-old orphan with 'Crab Affinity'.The apocalypse has come and gone, claiming humanity with it. All humans have had their 'Souls' stolen and claimed by monsters - vampires, demons, zombies - you name it.Reborn as Barnacles (Barns for short), the once-legendary hero claws his way back to strength under the tutelage of the gluttonous King Crab, a sentient crustacean with more vice than virtue in his shell.Follow Barns' journey as he rediscovers his power of rebirth, which when combined with a little 'crab magic' has the power to reset humans back to their original selves.It's time to take a crack at resetting the apocalypse.

Revisit the peak of the Olympian lore.... An eighty year old scholar who has been a fan of Greek mythology since childhood finds himself reborn as the titular ruler of the underworld, the death god Hades after a tragic death. But the gods of Olympus are very much different from what the stories say. He will have to navigate through his new life as a god and prevent a coming calamity... All while not getting caught... How does it feel to be a god in Olympus? A tale into the heart of myths.