Bokura no Kiseki

Our Miracle (ボクラノキセキ, Bokura no Kiseki) is a manga written and illustrated by Natsuo Kumeta.

Plot
Ever since young, Minami Harusumi has been having recurring dreams and flashbacks of his past life, Veronica, a princess of a small country called Zerestria. Thinking that getting reincarnated is normal, he told his classmates about it and was soon mocked. While getting bullied when he's in middle school, Minami rediscovers magic, something Veronica had learned. Reassured those memories are not merely imagination, Minami wrote what he remembers in a notebook so that he won't forget. And everything started to change when his high school classmates happen to read the notebook.