When looking at OP for Realm I tend to look at items that are not situational and can simply replace its counterpart with little to no negative effect. For example SDag has a great max damage and nice range but its minimum damage keeps it balanced. The CDirk Has incredible damage but low range. The Dbow is more interesting, as it DOES have one of the highest DPS in game and it’s hard for me to tell if the fire rate keeps it balanced… Compared to covert both of the UT bows are incredibly OP.
After browsing through the UT list, my pick for most OP item goes to Doku.
It is a direct upgrade to ninja and in honestly it is the item that makes the class remotely viable. The wavy shots are a negligible downside and its greater range, fire rate, and DPS make it outclass Masamune is every way. Maybe this is just a symptom of ninja as a class being tremendously under-powered, but Doku is not nearly as niche as a UT should be. It fills all roles for the class well and in that sense it is incredibly overpowered.