A sequel to Rune, known as Lost Kingdoms in North America, has been confirmed. From Software confirmed it is developing the title, and is promising its sequel will be an improvement over the original. There are plans to include over 200 battle cards, dozens of new enemies, and a new protagonist. The story has yet to be outlined, but word is that From is planning to overhaul various elements of the gameplay system, which won't limit players to using some special abilities during battle sequences.
No exact date for this sequel has been confirmed as yet, but it's expected that Rune 2 will be released for the GameCube sometime next year in Japan. There is no word on whether Activision will be picking this title up as it did the original Rune, and so a North American release is uncertain at this point.