That really was Ruka's sword. And someone did polish it while he was hospitalised. Of course, it wasn't Shiori.
Shiori went to Ruka's clearly labelled locker. The sword is identical to the one she draws from his chest for the duel.
Obviously, Ruka was on to all Shiori's bs from the start. He said that just to catch her in a lie later on. I mean, she clearly didn't know him before. She looked surprised to see Juri talking to him and showing him such respect, when Juri's usually just aloof and intimidating. Shiori is jealous of someone else being close to Juri, yet also intrigued by a boy who is so much like Juri. She intends to take Ruka for herself due to her jealousy of anyone else getting Juri's attention, as well as her urge to make Juri jealous, in kind. But, being the bi disaster that she is, Shiori falls for Ruka's charm, playing into his hand. Though I do think he eventually realised Shiori's true feelings for Juri and wanted her to admit it. He was upset that she kept claiming he was the only person she ever loved. Ruka knows he only has a few days and will step over anyone to achieve his goal, yet his goal is truly selfless. He only wants Juri's happiness, whether with Shiori or free of her.
Delving a little deeper, I think we can infer from the flashbacks and inner dialogue that while Shiori was at her other school with her previous beau/boy who liked Juri/purse, Juri progressed in fencing at Ohtori, and Ruka became her sempai and confidant. The two were very close and she probably told him something about her locket, (but likely not the who or what gender. I think Akio told him that in his sleazy Akio way.) while he may have hinted at his own unrequited love to her. Juri said she was only "filling in for him" as head of the fencing club while he was ill. We see from their fighting styles that he taught her all her best moves. Even when she's at Ruka's throat, he's still extremely important to her. She's thinking about him when he's gone/ dead to Ohtori's closed off world of immaturity.
The person who actually kept Ruka's sword polished, awaiting his recovery and return to the school, was Juri herself. I have always thought that. It's what Juri would do.