Seirei Gensouki: Spirit Chronicles

Rio is a ruthless orphan boy who lives in the slums. At just seven years old, he finds himself the reincarnation of Amakawa Haruto, a Japanese college student with a tragic past. While still reeling from this shocking epiphany, Rio also learns that he possesses extremely powerful magical abilities and uses his new powers to solve the girl's kidnapping case. Her achievements were recognized, and as a reward, she entered a prestigious aristocratic children's academy...?