Jump Ultimate Stars was a very popular game (overall in Japan) thanks to its big roaster, game mechanics and combos potential.
Maybe it went under the radar from some people because it never got out of Japan... but many people got it from different ways... (It also helped that the DS is retrocompatible).
Currently it is possible to play this again thanks to Wiimmfi (yeah, shocking Nintendo ending official servers right guys?).
Anyway our discord is getting pretty active as of lately, and the server not needing to patch the ROMs (you can play with original hardware) and some emulators like MelonDS being able to interact with original hardware makes it widely easier to play this day.
Here I share some YouTube accounts where you can see how we play this game:
If you want to give it a go be sure to join us in the Discord, or perhaps you are not interested in playing with others, if that is the case you can enjoy the main campaign as many folks find it very good too and talk about it there!
I bought Jump Superstars for the DS when I went to Japan in 2006. Ended up being one of my favourite games. I never got around to the sequel unfortunately so I might need to hunt it down
I was in Japan from 2008-2012 and had both games. Frankly, while both games were good, I remember preferring Super Stars even though Ultimate Stars upped the amount of just about everything. I think the thing was that partially due to the language barrier (I learned a good amount of Japanese while there but never became fluent enough to understand manga-type writing, lol), the simpler mechanics of Super Stars were easier to manage and the ton of stuff Ultimate Stars gave you was just overwhelming.
JSS was very neat the combined specials were awesome and sadly they didn't make it to the sequel, but it was a wrong decision to not implement wifi gaming in such a kind of game... that's why JUS thrived regardless of the difficult environment in which it was conceived...
I think it might be a bit difficult to get a physical copy of it... maybe you can resort to emulation for this.