These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Les Yay: Sio blushes her way through every conversation with Asao and risks her life to protect her, despite them barely knowing each other. Asao, for her part, seems to find Shio's geekiness adorable. Their interactions come off as very romantic.
Memetic Mutation: "RESPECT FOR THE DEAD MAN". The OP is a metalcore song, which is rare for an anime. People proceeded to go bonkers with it.