Cyberpunk: Ultimate Cyborg System - Chapter 173: Where Did It All Go Wrong?

Li Yubing and Tang Xue were deskmates throughout the whole six years of primary school. After being plagued by Tang Xue for the entirety of this period, Li Yubing saw his chance and broke free with his secondary school selection. With no contact for yet another six years, who knew that Tang Xue and Li Yubing would one day meet again in university…

- Description from Novelupdates

A man is reborn into the world of Avatar: The Last Air Bender as a waterbender from Katara's tribe. Best of all, he was the same age as her, and he had a system with him to help.He knows the future and a system that lets him continuously get stronger by completing quests or long-term missions, as well as giving him the ability to copy abilities from others for himself. He will become invincible in the world of Avatar, even more so than the Avatar himself.

Descent of the Phoenix – 13 Years Old Princess Consort

The strongest female assassin from a special assassination force met her death one day on a mission. To her surprise, she woke up in the body of a 13 year old girl, Mu Rong Liu Yue. Through Liu Yue’s past memories, she found out that she was bullied due to the huge birthmark on her face, even though she came from a renowned family. Liu Yue was beaten to death by her own cousin, and that’s how she managed to enter Liu Yue’s battered body. The assassin then decided to live her life as Liu Yue and swore to avenge her death.

- Description from Novelupdates

One day I got a younger sister.Only I know her true identity.