I would say the culprit has to be Takuma-san. My deduction is that after bringing the cat into the veterinary center, she could use the cat as a scapegoat for the blood on a weapon she is planning to use. Not only that, it is very easy to verify that she was at the vet center, which proves her confidence that the source of blood came from the cat. It is also very suspicious that she was carrying the umbrella in the first place, since it doesn't appear to be raining at all. So before Yamamoto-san entered the bathroom and after Kida-san saw Kujyou-san enter the bathroom, Takuma-san had much time too murder him in that time frame. After killing Kujyou-san, Takuma-san washed the blood off the umbrella using the local water fountain rather than spending too much time in the men's bathroom washing it off. Then after Yamamoto-san yelled that he was dead, she blended in with the chaos. The evidence should be an examination of the blood on the umbrella (as well as everyone else's stuff with blood). I would have more evidence but I'm not actually at the crimescene and this deduction is mostly conjecture.