To easily gain AP, if you are using a low level character, equip a Beckoning Cat (AP +100%, PP +20%, Gil +50%), three Diamond pieces of equipment (for example, Diamond Sword+, Diamond Armor+, and Diamond Shield+). This will give you another AP +100%. Purchase a large number of Diamond Rings (AP +300%, Breakability 100%). Equip one of them. Then using all of that equipment, fight a level 100 Exdeath on a day you will get an AP bonus (such as your bonus day). Make getting the AP chance your priority. You should score approximately 36 AP per fight. If you feel confident, use the same equipment/accessory setup as above, only substitute the level 100 Exdeath for a level 50 Chaos. The AP chance will be the same for all three fights (you can get it three times). If done correctly, you should score approximately 108 AP.