Okay i just finished reading v1 of the light novel version and let me tell you. There are some SERIOUS changes...like...SERIOUS.
I'd rather not spoil but here are two major stuff i noticed.
First, they changed how they spell Mizuki's name.
Second, They actually added non-existent stuff to the LN. Like....that second epilogue. I read a bit ahead of the wn but lemme tell you. THAT was NOT in the wn. sure it might've been possible but what they did in the ln was just straight up blasphemy. dont click the spoiler if you dont want major spoilers.