If a romance between an adult and a minor happened in real life, I'm totally for shipping the adult to jail. But it's hard for me to see Miku as a real teenager. It's an adult, writing in a teenager, that to me seems more like a college student than a high schooler.
That's probably why even though the "premise" is High School, it doesn't bother me, it's almost like they just got the age wrong. ¯\_(ツ)_/¯