In order to get easy AP, first collect as many AP% increasing items as you can. During a bonus day or AP day with all those items equipped, go fight chaos and try to get the bonus. If possible, you should get around over 200 AP in the end about 70ap a battle for 1 item.
When you play against chaos in battle mode, on your pp bonus day you would recieve 120 pp every time. You can keep retrying and get 120 pp every time you defeat chaos in battle mode.