There's nothing repeatable other than farming the highest difficulty treasure vault node and the Bleached Earth quest if you have it. If there are occasional battles with big sums the only one I remember is Tunguska, which I'm not even sure is available in the Main Interlude version if you didn't do the original. There might be more, but I don't remember any. If QP is the main thing you need just farm it in the treasure vaults. If you need something else more, farm that. It's a marathon with no shortcuts.

If you reach Ordeal Call, you can farm at Las Vegas Ordeal Call Free Quest. Do it 3 times per day, and in one week, you can get up to 105 million QP.

Also, it's not "marathon with no shortcut".

@Muhammad Abdul Aziz Habibi So to access that I need to finish Lostbelt in its entirety. Pretty tall order huh...

Yup. Either that, or doing Treasure Vault. You can also wait for events that can drop lots of QP, but it's not happen that often lately.

I wouldn't recommend speederunning Lostbelts just to access the OC Free Quests.

The QP amount isn't that much of a jump. Regular Treasure Vault quests drop enough as well.

Las Vegas OC quest is just better because of high Bond Points. If Bond Farming isn't a priority rn, you should take your time with the story.

The christmas event only needs Traum completion if you do main quest. Free quests are locked behind Fuyuki/anyone can do it realistically.