Wonderful post! I can't comment on the vocaloid aspect, I'm not familiar with that software, however:

Lyrics:
Even from 40 years ago, one can see important basic skills here: you identified English syllables with open vowels--those are the easiest for open-throat singing, and, at the same time focused on repeating rhyme patterns. Like songwriters who have successfully attempted to write lyrics in a 2nd language, you used craftman-like care to understand the vocal sounds of certain words to make the song singable---very impressive Shigeki!

Also, several lines are slightly riske' ("we'll get naked, completely")!! But this, also, is seen when writing in a 2nd language; it's difficult to grasp the slight connotation differences between languages, so that is perfectly understandable!

Production:
I listened to both, and here is my suggestion: you should make a "duet" version! At a modulation point, introduce your original! Anyway, I liked both alot.

Thanks for sharing your work, old and new!!