There's another easy way to get a lot of orbs, this time on the game's seventh mission. Better yet, it will only take about twenty seconds to get about 4,000 orbs. At the beginning of the mission, break the egg-like objects to your left. Then, head forward to a tunnel and break more of the same egg-like objects. Turn right at the end of the tunnel, and you'll see a gem. Execute a streak with the Exceed Gauge full, and then immediately use the Devil Trigger and combo it. When the gem finally breaks, you should have around 4,000 orbs. After that, all you have to do is retry the mission and do it over and over again as needed.