Since the best polished thing & costed most of time to be made in my game - the combo system of Characters - so far has no one succeeded in doing it, and it was my fault to not proper explain to player. Therefor, i will explain about it in detail here, so new players can do it easier.
For an Actor to perform Combo, these condition must be met
1. Has enough of AP: while in Battle, at the mid left corner you will see a window say _ AP: 3 AP (Action Points) is required for Actors to take any action. Except of Ultimate Skills, another Attacks/Skills only cost 1 AP
2. the Weapon must have CP (Combo Points): CP is shown at the bottom line of item's description
- And you can find a quite strong weapon with 3CP for Mei at right most corner in the Dangerous Cliff's below map
Now, once you got the right weapon, simply perform attack . Once your attack has landed on enemy, a Pop window will show up to indicate that it's the time for you to input Combo (you will have like 1 second to press the keys).
Combo's Keys can be checked in Actor's Skill Menu
And since the game use AP (Action Point) mechanic. One actor can take as many action he want as long as the Party has sufficient AP.
* To switch between Actors in Battle, you can either press U/ O key
* To end turn and save AP for next turn, you can press X and choose > End
That's it. Hope you guy can try out the Combo system now =D