It's quite impossible to just give 1 song so I'll give one per album.
A song for XX : A song for XX
LOVEppears : WHATEVER
Duty : SURREAL
I am... : tough but i go for
endless sorrow
RAINBOW : Rainbow (even if its ont A BALLADS)
Memorial address : Because of You
MY STORY : the hardest one !! I'll say
GAME
(miss)understood : fairyland
Secret : kiss'o kill
GUILTY : decision
Next level : sparkle
Rock'n Roll circus : microphone
LOVE songs : crossroad
Party Queen : tell me why
FIVE : brillante
LOVE again : sweet scar
COLOURS : lelio
A ONE : warning
Made in Japan : Mad world
sixxxxx : sayonara