Take a listen. It's really well-made and maybe even professional.

This is amazing for a fan opening theme

It's amazingly made, but it's not jelling with me for some reason... just doesn't seem to fit with KH. 

i like it. it's nice but personally i prefer it on ending / credit scene since it has slow tempo. we are all familiar with Hikki's simple & clean / sanctuary as OP for years. those songs has beat-like tempo which is suitable for fast-paced screenplay. and i will feel weird if KH3 OP isn't either simple & clean or sanctuary.

*i don't know much about music so i don't know terms using in it. 

The lyrics are pretty good. I feel like the primarily focus of the song shouldn't be Aohana however. The singing is very well done, so is the production... Even though it sounds a bit corny at times. I feel like the instrumental would introduce a bit more modern pop techniques such as rolling hi hats or distortion in the beat or something so it doesn't sound so early 2000's. This would work better as an ending song simply for the pace. Overall really good attempt, especially for it being fan made

Wow, this was definitely well made!  I could even feel the Hikaru vibes in this Youtuber's voice!  Overall, the somber tone fits the situation in terms of Kingdom Hearts III, since the stakes will be high in the final chapter of the Xehanort Saga!  Overall, great fan-made intro!