[Ultragunner]

^

Spoiler for :

Mayumi only guessed Tatsuya was an "Extra" - those have been striped of their name from the Yotsuba. It is not mentioned in the LN, but perhaps she did make the same connection with Miyuki as well. I don't think she has shared this with anyone, even her father because she feels it is inappropriate to pry into others' background

About the scene of Miyuki and Tatsuya, it's actually in a special story that hasn't been compiled into any volumes yet. IIRC, it takes place after the Yokohama incident (vol 7), well it's a Halloween party