I love your character design! It is a shame that you weren't able to add a
tail. I'm knew at this whole Build-a-Vroid thing so I can understand the
whole "how do you do this?" issue. I suggest going to Booth.PM and look
up *Animal Tails Pack*, sadly its not free but not too expensive. The
standard pack is 500 Yen (roughly $4.10 in US money) and the Extended Pack is 1,000 Yen (roughly $8.19 in US money roughly). If you're unable to spend money like that, for whatever reason, I totally understand. (Like, me neither dude 〒v〒 lol) And I would suggest making your own with the help of this YouTube Video. I found it helpful, hopefully you will too.
*How I make tails in Vroid studio* - YouTube
So from (this very new, fresh out of the womb complete noob) of a creator
to creator. Good luck and I wish you and your glorious Vroid of a Cat Man well.