Does 海半仙 have an English translation?
In chinese,半仙==半+仙==half+fairy(generaly male)。Generally, 半仙 is a human but with some magical power, rather than a ghost, the 半 means a half, not a entire fairy（because He is still a human）.

The adjective 海 in 海半仙，most probally the place this 半仙 lives is close to （OR in） a sea or lake （waterside）. It can also be a family name of 半仙, but mostly is the place relating to water. 

You may encounter 陈半仙，where 陈 mostly is a family name, because 陈 in China is a very popular family name, but 海 is not