Thanks for the nice response :D (though, for-real, I am astounded you always manage to say something nice about my works. Any honest criticism is also fine, don't worry :)
I agree that the "modulation of a tone each time" is a simple trick to re-use a theme multiple times without it sounding bad. Here, the bass and rhythm could change without any change in the melody, hopefully making the transition sound decent!
The 'abrupt end' is actually a loop to the start, which is why it sounds so abrupt! It is actually 'finished' in the sense that everything is there - the 'demo' part is only because... I am not satisfied with it yet, hihi.
"you have a real melodic talent": THANKS! That means a ton coming from you :D! I would like to think I am decent when it comes to making chord progressions and melodies, but I just suck so much in the mixing and mastering department that it still manages to sound 'barely functional' haha. Thanks again ;)