Toaru Majutsu no Index - Volume 1, Chapter 3: The Grimoire Peacefully Smiles. "Forget_me_not."

Before Wufu was reborn, she had no idea there was such a thing as rebirth. Only after her rebirth did she realize Heaven must have thought her previous life was too smooth, so it sent her to suffer in this ancient land where morality, decency, and the Female Precepts were held in high esteem, pitiful indeed! From being a master jade carver to having her soul transmigrate into a farm girl with a wretched background, she was bullied and humiliated. Even the bun-selling mother advised her that forbearance is gold? Bullshit! She could endure, but her other identity absolutely could not—robbers, swept away; insults to her mother, you're crippled... Wufu has a saying, for every insult and humiliation, I will repay a hundredfold. But what's with this one? He doesn't bully her; he only wants to sleep with her? And he even dares... to mount her? Well, a lord can endure, but Wufu cannot. Mount him back, life or death, a hundred years, neither owes the other anything!

It is an era of artificial superintelligences, interstellar travel, gene medicine, and virtual reality worlds. Far into Earth’s future, 15-year-old Gu Ding is a student of Cerulean Military Academy by day, and tavern waiter by night. His ambition: Become the space pirate with the highest bounty offered by the Universal Federation Government. With the help of Neptune, a neonate super-intelligence, Gu Ding finds himself thrust into a galaxy of shadowy organizations, political underdealings, and otherworldly forces that lie beyond human comprehension…

Thirty-three classmates hold a reunion after graduating. Tensions soar and old friendships are tested, as a strange turn of events lead them to follow the path of the ancient gods.