This mission will have you facing Mira, one of the two people who are corrupting time. He is strong, very strong. However, you don't need to actually kill him to finish the battle thankfully, and he tends to be very defensive while fighting. His energy attacks are very powerful though, so if you see one coming, make sure to block!
If you are rushing through the campaign, this battle can be very tough. It's suggested you level up through some Parallel Quests, or come equipped with a few healing items to help with this fight.