A very great game, based on skill, power and luck.
I was ultimately lucky on this one. The boss killed Nathan, Dori and Luke, and leaving Mirinda from almost to no HP. I used Mirinda's limit break, and luckily the boss was also at really low HP, and got defeated.
Now I'm going to include a good strategy for those who want to beat this boss:
First, have Nathan, Luke and Mirinda use all their limit breaks at once, then let Dori use Ultimate Power to boost up the power of those limit break. You could deal 10000+ damage with all three limit breaks! You would want to be a little lucky to have Dori still alive until when the boss is at low HP, or if possible, have her alive for the whole battle. If Dori is defeated (and when the Boss is at low HP too, this strategy could only work), have Nathan, Luke and Mirinda spam limit breaks. If you have only one person left, hope that the Boss doesn't use the instant death attack OR kill the last ally before the ally kills the boss. Mirinda does have two ultimate limit breaks, which is Rain of Ice Stone and Dark Shockwave, and Luke has Layer Storm as his ultimate limit breaks, which can only be accessed when HP is very low(maybe almost to none..) Not sure if Nathan has any though....