SD Gundam Battle Alliance uses Oodle Kraken compression. Despite the fact the game does have a hexadecimal key, the UCAS / PAKs aren't encrypted so you can just use oo2reck:
Code:
Compressing 1 file, 102,797,664 bytes
Compressing pakchunk5-WindowsNoEditor.ucas
Compressed 1 file, 102,797,664 => 329,446,054 bytes. Ratio 320.48%
Compression time: cpu 0.20 sec/real 73.46 sec = 0%. Speed 1.40 mB/s
All OK