Ruolong Bai

Bai Ruolong is the disciple of Ziz, a Magus from the Wandering Sea who he refers to as "old man". He was Ergo's best friend before Ergo lost his memories. He and Ziz didn't have any plan to claim Ergo because the Wandering Sea was the last in line and they were both fully expecting the case to end on Wuzhiqi's turn. (Source: TYPE-MOON Wiki)