Yea, such big age gap is unconventional, and yeaaa the boi is a freakin minor. But so what? Mizuki respects Akari a lot. They've got better relationship compare to those who are at the same-age relationships. Respect, understanding, and love, that's what makes a good realtionship good. Not some stereotypical and prejudiced standards set by the society.
The extreme calmness of the story subtly agitates and makes my heart nervous because I never know when and what kind of bomb might suddenly drop as I peacefully reads the story. I can never be too assured, given how extreme the other stories that I have been and have read.