Here is the full list of all 26 GUNBIRD 2 achievements.
Stage 3 clear
Stage 2 clear
Stage 1 clear
Upgrade the shot until maximum
Watch the ending with MARION
Watch the ending with TAVIA
Watch the ending with ALUCARD
Watch the ending with HEI-COB
Watch the ending with VALPIRO
Watch the ending with AINE
Stage 4 clear
Stage 5 clear
Stage 6 clear
Stage 7 clear
Watch the ending without continuing in BABY mode
Watch the ending without continuing in CHILD mode
Watch the ending without continuing in VERY EASY mode
Watch the ending without continuing in EASY mode
Watch the ending without continuing in NORMAL mode
Watch the ending without continuing in HARD mode
Watch the ending without continuing in VERY HARD mode
Collect maximum quantity of bomb (default setting)
Increased life
Obtain more than 50 bonus items
Clear the stage without destroying any enemies
Unlock all achievement