To barely lift the sword, you need a minimum of 50,000 Dourikis and to swing it at normal speed without it being really really slow, you will need at least 500,000 Dourikis. To swing it at a very fast speed like a powerful swordsman would require at least 5,000,000 Dourikis. So at 10,000,000 Dourikis or more, A person should be able to use it extremely effectively in battle. (Think Bui from Yu Yu Hakusho he had this huge axe bigger than himself yet he was able to move it pretty fast)
Which parts of my character aren't you sure about?