I applied some google-fu, and it resembles a piece of samurai armor this website calls a "tekko". I think the kanji is 手甲. Google translating the Wikipedia page confirms the method of attachment. I can't find any clue as to whether the hanzi would also be 手甲 from here; will have to google more. It's annoyingly hard to find info on Chinese history in English compared to Japanese.

The closest English term would be a demi-gauntlet, but that doesn't really fit what Zhu Jiu is wearing at all.