What is the relationship between Akiyama Riko and Shuicheng Xuefeng destroyer?

Senior year and junior year. In the magic capital of Tokyo in the near future, the destroyer Shuicheng Xuefeng, which protects mankind from evil, volunteered to join the stealth mission with her predecessor Akiyama Riko in order to rescue her missing mother. Riko in Akiyama and the destroyer Xuefeng, a water city, are the relationship between their predecessors and their successors. Akiyama Riko, the pole before Emily appeared, skill wind cutting, meteor, jumping/space cracking.