Enix had a lot of investments in the creation of manga (and to an extent, anime) before Square ever came along. I guess the union's strength and the popularity of the manga allowed the anime to be made so soon, and to be followed by the PS2 and GBA versions.
That said, this game is quite nice. Not the best GBA RPG graphics ever, but certainly well done, and the music is more than passable. Combat is nice, sort of like Final Fantasy, I suppose....but the magic/alchemy system looks like it's going to be hell to use for someone who isn't Japanese-literate, especially since you can apparently use spells outside of battle, so they most likely will be needed to solve puzzles and such.