This Devil May Cry 5 (DMC5) Exploit lets you farm infinite Red Orbs. You can get around 85,000+ Red Orbs per Minute which is 5 Million per Hour.

It works like this:

1) Play to Mission 13. Here you unlock the Dr. Faust hat (a ranged weapon).
2) Buy Dr. Faust Level 4 Upgrade (if you can't afford it get Level 2 or 3 for now and upgrade later).
3) Play to the last checkpoint of Mission 13, where the Divinity Statue is. Then drop through the hole to where the 4 Monster Nests are and you're supposed to destroy 4 Blood Clots.
4) Equip Dr. Faust (ranged weapon), go in Ranged Stance (D-PAD LEFT), lock on to enemies with R1/RB and press CIRCLE/B to attack. Now just keep pressing Circle/B. Make sure you have Auto-Assist DISABLED in the game options.
5) Defeat all Enemies. Then restart checkpoint and repeat. The Dr. Faust weapon sucks the Red Orbs out of the enemies and makes a lot more Red Orbs drop. The higher your Dr. Faust Level the more effective this will be.

With Level 4 Dr. Faust it gives around 85,000 Red Orbs per Minute on average. That's over 5,000,000 per hour!

With Level 3 Dr. Faust it gives around 36,000 Red Orbs per Minute on average. That's 2,160,000 per hour.

Buying all skills costs around 4 Million Red Orbs per Character which is 12 Million total. So you need to farm for a little over 2 Hours to buy everything in the game. It's also good to farm some Red Orbs before Dante Must Die difficulty so you can use them to pay for revives.