Super spoilers for people who have completed this but haven’t read the webnovel.
There is a huge amount missing from the comic. But one of the biggest and kind of most impactful things is that mugetsu is mio’s little sister.
Don’t know if it’s just pure mtl, or if the author themselves are horrible with grammar but this is too hard to read. The sentences don’t flow. Fortunately the story itself doesn’t seem very good so I’m not missing anything.