Kagijin

According to legend, a war between the "Kagijin", beings of fearsome power, laid waste to the world and buried it in sand. Time moved on… and now, Chiruda Portman, a female soldier of the Gabbia Empire, has been ordered to exterminate a certain man.

The name of the boy is "Tsubame"!

The two meet by chance, but Chiruda senses something strange about Tsubame, who loves freedom and reading books... what is the big secret he holds!? A new-age fantasy of their adventures set in a breathtaking world!! "

(Source: Shounen Jump)