To gain access to each characters Voice Gallery (and the ability to choose their selection pose) you need to win a certain amount of fights with the required character. Story, 1P Battle and Survival are all OK for this.

Gallery	How to unlock
Alty Al Lazal Poses/VA Gallery	Win 44 matches.
Danzaivar Poses/VA Gallery	Win 42 matches.
Erel Plowse Poses/VA Gallery	Win 49 matches.
Gally 'Vanish' Gregman Poses/VA Gallery	Win 37 matches.
Ihadurca Poses/VA Gallery	Win 84 matches.
Kakurine Poses/VA Gallery	Win 44 matches.
Keiya Tempouin Poses/VA Gallery	Win 60 matches.
Lindwell 'Lie' Rainrix Poses/VA Gallery	Win 60 matches.
Midori Himeno Poses/VA Gallery	Win 50 matches.
Setsuna Saizuki Poses/VA Gallery	Win 46 matches.