Harald is the character grouped with Xebec to make a duo. Oda pretty much redid the scene with Roger and Wb drinking with Rocks and Harald,with the will of D characters revealing their real name
And again, Xebec pretty much only really respects Harald for his strength. They don´t really have much in common aside from that. Xebec has wanted to ally with him(not make him a subordinate) since they had an equal clash in Reverie, hyped by the narrator.