Seirei Gensouki: Crónicas de los espíritus (2017)

Blurb:
Rio is a run-of-the-mill seven-year-old orphan from the slums who serves as a lookout for a local gang. Yet when he falls into a fever, memories of a past life surface. After the gang shoos him away from their hideout to celebrate their latest haul, Rio wanders into town, still coming to terms with his new memories. There he crosses paths with a group of nobles looking for a missing girl. When Rio returns to the hideout, he finds the gang slaughtered—and the perp’s still around! What’s worse, the gang’s haul was actually the girl the nobles were looking for. Rio has to combine the martial arts from his memories with the magic power of this world to fight his way out of trouble and save the lives of both the girl and himself!

Source: www.anisearch.com/manga/35781