Recently, I returned to Hokkaido to do a contract, cotton mouth to try to improve my times. I thought I would start in the morgue and smuggled in the white katana. As specified dressed as a motorcyclist & melee with a Katana. Once done I left the area. I failed the mission stating I had to use a Katana. What is the point in being awarded items for my inventory when you cannot bring them onto a mission? after all it is a katana.
Dejavu. This challenge was made for Hitman 2016. So the items you can bring in now will not count towards the challenge. I’m pretty sure you have to get the katana (either start as the Ninja or steal the one from Yuki Yamazaki’s Rm). Unless we have an actual katana from which to choose in the planning stage. 
Try that if you want (and can), but to be 100% safe -source it from the mission itself.
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You have to use just the plain katana. Not any other version or variation of a katana, but just the regular katana, either brought in or found in Yuki’s room.
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Or perhaps you brought the masamune? That’s not categorized as a katana unfortunately.
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Hi
Thanks for the reply, I have all Katana’s i used the white Katana.