Like Starikun said, in Kimi no Shiranai Monogatari 0:34-0:38 was one of the highlights of the song, and in a similar vein, so was 1:50-1:54 (which is the same notes but in a different stanza). Those spots were where I could hear that you were comfortable and confident in your voice, except where at 1:54 you maybe ran out of breath? and the pitch slid down a little.
Some advice that I think will benefit you in confidence, diction, pitch control, and overall tone would be: learn to breathe. Singing requires a special kind of breathing, from your gut, and it's a kind of breathing that people don't do much nowadays, so you have to learn how to do it. There are many guides (such as here and here and here) that teach how to breath properly in order to maximize airflow and give your notes support.
I also used to be uncomfortable with my lower range, and one thing that has really helped is chanting. I pick a note at the bottom-ish of my range (for example, G) and just recite something while holding that note and trying to sustain a steady one without straining downwards. For this purpose I usually use the heart sutra, but I'm sure any chant-like thing will do.
As for high notes, you have them, but you have trouble sustaining them. Correct breathing will almost certainly give you help in this regard.
In the song, especially at the beginning, your pitches were all over the place. Before uploading your songs, you should listen very carefully to your recording and note where pitches are off, and if you can fix them on the next try or it's just difficult to fix. If you're consistently low on a note, raising your eyebrows on that note can help you fix it. I don't know any tricks for going too high consistently though.
Your rhythm was also off in the beginning, which indicates to me that you didn't practice this song enough. Be a perfectionist. Record yourself practicing and listen to it and note down which parts are good and which are bad and fix them one part at a time. Practice the same line over and over until you get it right, and then you can string it all together. If you get sick of listening to yourself when you review your recording, then who's going to listen to you, right? Make something that you want to listen to.
Your pronunciation could also use some work, but my greatest concern about your pronunciation is that some of the words were just incorrect (such as saying "saru" instead of "suru"), which is something I do a lot when I forget the lyrics and I just say something random instead. Again, that's a sign that you need to practice more. Read the lyrics out loud, slowly, get them perfect. Listen to the original and how they say those vowels. Get your tongue and lips working to automatically say the words correctly, and then you can focus on making beautiful sound.
This was very long, but I hope you'll be able to fine-tune your recording process and continue on your path! :)