Let me just put this out there: it seems like this is a first project created by middle/high schoolers. If that's the case, congratulations on getting something finished, that's more than most people manage, but you've run into a lot of classic problems that come with inexperience.
I'm not going to lie to you and tell you this is a masterpiece, but I am going to try and be constructive so that you can use this to better your skills going forward.
Art:
The art style gives me very strong MS-Paint vibes. In all honesty, it kind of hurts my eyes to look at. I'm terrible at drawing so I can't really give you a lot of tips in that regard, but one thing I would recommend would be to use a pixel-art style if you're struggling with adding detail. I know it's kind of cliche at this point, but it's cliche for a reason. Another recommendation could be to draw in a program that supports anti-aliasing, so that your lines don't look so odd and sharp.
Story:
The story breaks pretty much the two most fundamental rules of storytelling in the first five seconds. Show don't tell, and don't bombard your audience with proper names without giving them time to adjust. I read the pre-game text screen but my guess is 90% of people won't even do that. If you want your audience to read, you should keep it short and interesting. You don't need to present all of the background world-building to your audience upfront. The fact that your character's full name is "Lalaisa" but she goes by "Laisa" is not something we need to know as the first piece of information we're given. If you were telling a more in-depth story you could present that detail naturally by having one of her friends call her "Laisa". Why do we need to know all of the details of who is part angel and what relationship they have with each other? More specifically, why do we need to know these details upfront? You should limit the story that's directly told to the player through the voice of the author to information that's absolutely critical to understand. Having the character be part angel is cool and all, but do we really need to know that? What if we rewrote the opening scene like this:
[Opening text screen]
There are very few celestial beings who reside in the mortal world, and those who do tend to stick together. Lalaisa and Yngar exemplify this, both being half-angels and lifelong friends. As a mage and a monster hunter, they've been known to lend a hand to one another in their hour of need.
Recently though, tragedy struck. Yngar's fiance sadly passed away.
Three weeks later, Yngar rides out to find the nest of the beasts that have been attacking the local village...
[show scene of them talking]
Lalaisa: Promise me you'll be careful on your hunt.
Yngar: Sure, Laisa, whatever. I gotta get going.
Lalaisa: Are you sure you don't want me to come with you? With my magic and your skills we do make a pretty good team!
Yngar: No! Look, every time a half angel does magic it drains their life force. I don't want you throwing away your life because of me. And... I really don't think I could take losing someone else.
Lalaisa: Yngar...
Yngar: Besides, I could use some alone-time to clear my head. I'll see you when I get back.
Lalaisa: Come home safely...
[Yngar rides off]
["A few weeks later" appears on screen]
Lalaisa: Where is he? He should be back by now! [one of the monsters walks on screen] Huh? This is the same kind of monster Yngar was hunting! Maybe I can follow this beast back to its nest!
Just as an example, I think at least that this would be much more compelling. It would take more work to create, but not much more since you could basically just implement it like a slideshow and have it display a series of images.
Gameplay:
Most of the gameplay problems come down to technical issues and game feel. I don't feel I can accurately provide any insightful feedback since most of that is either stuff that comes with experience or problems that you probably knew about but didn't have time to fix. One piece of advice I can give is this: if you're going to use a game engine like Unity you should take advantage of the tools that it gives you. It feels like you're setting the characters' velocities/positions manually when it has a prebuilt physics engine that you could use. It just takes a little bit of reading up on the tools you're using to understand how to apply that to your own projects.