Seirei Gensouki: Spirit Chronicles.

His past life and current life are intersecting--a boy with memories of two lives faces his destiny! After his mother was killed at an early age, the orphaned Rio fought his hardest to survive in the slums. One day, he awakens to the memories of Haruto Amakwa, who died in an accident while dreaming of being reunited with his childhood friend, and Rio realizing he has reincarnated in a world of swords and sorcery.