I didn't quite realize how far this series had gone. Not far past 1998, but still, for a PC-fx origin game, it's quite something.
As far as I can tell, there was:
Blue Breaker: Ken Yorimo Hohoemi o (PC-fx): Sep 27, 1996
Blue Breaker: Ken Yorimo Hohoemi o (saturn): Nov 27, 1997
Blue Breaker: Egao no Yakusoku (PS): Dec 25, 1997
Blue Breaker Burst: Bishou o Anata to (PS): Jul 23, 1998
Blue Breaker Burst: Egao no Asuni (PS): Sep 10, 1998
As far as I understand:
The first two games (PC-fx, Saturn) are largely the same game.
Egao no Yakusoku is *more or less* the same game, with several added scenarios.
The two "Bursts" are fighting games, and seem to be super similar - they even have the same HUD. but the second game appears to have 2X as many characters.
it's clear the franchise didn't exactly set the world on fire, but not bad for a game of PC-fx origin - it probably has the most ports and sequels of any PC-fx game!