Actually both are Nana's swords but as you can see, the one that Junna holding has a green gem on it. It because in the Revue Starlight Gekijouban Movie, in their "Revue of Hunting", Nana had breaks Junna's bow and the green gem on her bow fall off. Nana almost defeat Junna by forcing her to "kill her self" with the Wakizashi (the shorter katana). But Junna decided to take the Wakizashi from Nana, crush the yellow gem at the end of the sword handle and stick her green gem on to it. So it became her sword.