The story is written as though the MC found a way to connect to our world from his own. This means that the story is written as though the MC has decided to publish his own adventures.
The first chapter is in 1st person and acts similarly to author notes written by the MC, but aside from that, most of the story will be written in 3rd person. The only exception to that is the in-between, when the MC reincarnates again, and when he decides to reply to comments. The Harry Potter adventure is written as though it has already happened from the MCs perspective, but future adventures readers may be able to influence.