I haven't fought that fight in a while but I'm pretty you can guard at least the majority of his combo, and to get the reaction command is just to keep running when Xaldin does his jumping attack to stack the reaction command.
My advice would be that when he attacks, guard and mash the triangle button to get those sweet reaction commands to whittle his health down immensely. This video shows how at 27:57.
Also, in case you are interested, during the Data Battle, when he jumps into the air and is shooting his lances down (not his desperation move, mind you), Dodge Roll or Quick Run while also pressing triangle. A better idea is jump and mash triangle for each time he does it. This video can help (the technique here is demonstrated at around 43:03).