OKAY so i've never seen someone actually talking about all the cold stares shinoa gives to yuu when he mentions Mika or is with him. This happens with mitsuba and yuunoa too. There are a few panels where yuu and shinoa are together and mitsuba is just staring with kind of a sad face. What surprises me is that shinoa actually looks TOO serious. -
In chapter 15th, shinoa is explaining to yuu what happened on shinjuku battle which is serious stuff and she was with the same happy and sassy face as always til she notices yuu wants to talk about Mika. She changes her face and asks it herself if he does want to know and yuu gets surprised that shinoa read his mind
Yuu asks for her to tell him what happened to Mika. Nothing much happened to him, he just went back with the vampires and is safe, that is a good thing right? Shinoa for some reason didn't want to tell Yuu. "I don't want you to get too excited" "i really don't want to tell you..." it sounds as if she know what yuu's reaction is going to be like yet she doesn't want to accept it. And when she tells him, what yuu does is gently smile and blush a lil and Shinoa once again gives a cold/sad stare
Then, in chapter 17?? Im not sure lmao yuu and shinoa meet and yuu was too focused looking at sanguinem, he didn't even notice shinoa's presence and she is aware of it. In the third pic her expression is even scary wtf. Then yuu tells her and asks her to help him get mika back and does the same thing with guren and we get a panel of shinoa's reaction. It could be kimizuki's, mitsuba's... But no. It is Shinoa's. The fact that she asks "bc he is your family" could be bc she wants to make sure it is for that reason or she's just wondering how important a family member is, but she already got a lil familiarized with that concept so i'm not too sure
And in chapter 55, we get another time shinoa reacting to mikayuu, now in a more explicit way. We got small hints but this chapter is a big big hint that shinoa knows how important mika is to yuu and how much he loves him. I can even assure that shinoa thinks that yuu loves Mika in a romantic way and not a familial one and that she isn't as important to him.