Ignore the 3.4 score is just me being honest because by no means this fanfic is bad.
Writing quality: I give it a 3 because of this being write as a hobby and the author clearly being new to this doesn't check or edit and there some confusion of the usage of a and an which is fine one can easily understand. Secondly the usage of - name: " blah blah" doesn't fit well with the webnovel format but that's fine. Others minors details but meh.
Story development: not much to say I quite like it but to little chaps to make a full opinion.
Character design: I just love them and I am bias.
Updating stability: as already mentioned the author writes this as a hobby and when he feels like it so don't put to much burden to the author, instead be grateful hehehe.
World background: not much has been explore but it's marvel what do you expect there's a lot to explore.