Hollow Regalia, Vol. 2 (manga)

In a world where Japanese people were almost completely wiped out…Tasked with taking out the leader of the Moujuu—the Kushinada—Yahiro and his party have ventured deep into the ruinous 23 Wards. They’re greeted by two shocking sights: a vegetable garden and a Japanese girl riding a Moujuu. Yahiro manages to talk with her—until they find themselves under siege by RMS. Whoever this girl is, she matters. Now, if only she and Yahiro could get on the same page…!