Mark with Japanese Mark: 水府住　貞久 "Suifu ju | #458416

水府住　貞久 "Suifu ju Sadahisa". This mark is from a fuchi and was made by Sadahisa, who worked as a sword engraver (soukenkinkou) in Hitachi Province (present-day Ibaraki Prefecture). Soukenkinkou is the Japanese name for metalworkers who design accessories for bladed weapons. A fuchi is a ferrule that is placed between the tsuba and a sword's hilt.