This appears to be Fujimoto Yui adding her own blood to her sister Nao's...thermos? I think that's a thermos? It has Nao's name on it for sure. I don't know why she would be doing this, but it seems to me to imply that this should have a self-harm tag and therefore a higher rating than General. I'm not confident enough in this assessment to do so myself, so if someone can confirm that this is what should be done I'd appreciate it.
(It's also possible that this is Nao adding blood to her own thermos, but as a child her hair is shorter in the back than Yui's, around neck length, so I doubt it.)