Dang it you have no idea how excited I was to see this topic.
I also spoke with Mioku about the Totsuka sword recently, since I've been trying to get him to fight me for it for years. He said he was planning to give it to someone else in Kiri soon though he would not say who, which was smart, since I'd have tried to get them assassinated.
Anyway I suggested to him hey, instead of just giving it to someone in Kiri who will maybe use it one time as you have, you could put it up for a grabs in an rp event for anyone who is interested (many I am sure) to have a shot at it. He seemed pretty into the idea and actually said he would talk to YOU, Kamui, about doing that.
So as you can imagine when I saw the topic title and your name I thought he had actually went and pulled the trigger on it, but alas, no.
As for your question no you cannot strip them of it. You do not need to have evidence that you used the item IC, normally, as that is not part of the activity rule. The only reason that happened recently with Kiri was they had the swords claimed by "Sealed" on the claims list, and as there was no one by that name on the site, the swords were up for grabs. They claimed Gitsune was the owner of them during the time in question which is why proof was requested. Under normal circumstances that is not required, the person who owns the item merely has to log on within the period of time. Mioku has been doing that (trust me I've checked).
I'd suggest looking for other avenues of attack in regards to getting the blade, feel free to pm me if you want to hash out ideas.