Some of the sites I've seen listed Ys as a HuCard (II, III, IV), but maybe I saw something wrong. But I did see the Book of Ys for TurboCD. I don't know, I just badly want to find Ys again.
The TG16 was a great system. It's also argueably the the best (graphics-wise) system currently emulated well on the GP32. I highly reccomend checking out more than just Bonk's adventure when and if you put GPEngine on your GP32. Search this board. There's at least one thread somewhere about the best TG16 games.