When you use a weapon that you've equipped on during battle, various skills of the weapon will increase. If you get it increase to a certain point, you will be able to learn "Weapon Skill".

*Weapon skill is for close combat only.
 

etc...

TACTICAL POINT

To use the Weapon Skill you will need to gain Tactical Point (TP) by receiving damage from enemies during the battle. 

You can keep maximum of 300% of TP. Once you have used the Weapon Skill, TP will be back to 0%

If your TP has exceeded 100% when you attack or use a Weapon Skill, it will add-on to the damage to the target you have chosen.

TP is different from HP and MP, if you don't use it for a long period of time, the bar will decrease a bit by bit. So use TP Tactically to kill the enemies.