Continued..
During her death throws Rika said Hanyuu name two times. First time her character's name is mentioned. Hanyuu has not been shown yet visibly in the series as of this point but she has already interacted with everyone at this point.

The reason why I put spoiler tags in these comments is that these are spoilers for a scene as well as a mention/hint of something that could give away a lot to those who are paying enough attention at this point :P

Oh man this is actually the wrong screenshot.. and I deleted the correct one.. Bleh..

Basically Shion thought that either Rika was a body double and/or Rika herself was trained as an Assassin. Shion basically got REALLY lucky when Rika attacked her. She also managed to use the needle Rika was going to use on her. The stuff has a very nasty effect that will eventually cause the one infected to claw their own throat out. Before that part triggered Rika managed to regain her footing but at that point there was not much she could do. So she grabbed a knife.. Shion thought Rika was going to use it on her.. But no.. She used it to try and kill herself with the knife before Shion could do anything. It only half worked as she was still kinda alive before the poison fully kicked in.. Was a nasty way to go but better than what Shion had planned for her.