AniDB

Well, it is depending on your underlying definition of "sequel". Much like Final Fantasy, where the next one can be called a sequel. But, I use the one on the the Add Relations Page: sequel: Direct continuation of the story. prequel: Story that happens before the original. But, I can under...

Currently, Kakyuusei (1999) has a prequel-sequel relation to Kakyuusei 2.

Kakyuusei 2 is not a sequel to Kakyuusei (1999). Setting and characters are completely different. There is no connection between the storylines either. If any, there would be an "other" relation.