Im inthe underworld and theres a door with a weird thing with circle around it and its gold and it says it seems to respond with oni power.
please help ive been stuck for 3 months on this part.

it sounds like you need the next weapon, which is a hammer and is a gold color. The door looks similar to ones that you've seen earlier, right? Like the ones that you opened with the ice spear but just a different color?

Im not sure exeactly where you are right now, but if you dont have the hammer yet you need to advance farther in the game. You will come back to that spot later on
Hope this helps. If not, explain the place your in in more detail, and I'll be able to help for sure

u mean the Dokutosi Earth hammer against the Earth mozoin then yes

i remember onimusha 2 i havent played that game for over 3 years so i started playing it today and after a week i got 100% for all characters if u need help i can make a video to show you how to do if you are stuck or need to get an item. =P