What an "Angel of a Boy"? Like Hell you know your guys, Sensei-chan...
He's actually pushing her over the edge of the Abyss.
And Miku probably realized she missed out a few things...
Also, the family's reaction is funny - Mom and Nee-chan seem surprised by how familiar Sou adresses Yuri. Sakura on the other hand had long since realized who the hidden boss mob in that class actually is and who will become her new Onee-chan in the future.