Could somebody explain exactly what these items are for and what benefits they provide? Do they count only towards the boss job you are on or do they carry over on to other boss jobs?
Each Power Attack that is unlocked and gives you more strength against the Boss when attacking them (numbers for the current & next unlocked power attacks are shown on the Boss Battle page). Once the Boss is killed it will reset back to the first Power Attack and you can unlock them again in the next battle!