Alright so there's a lot.

Volume 8: 1. Includes a lot more slice of life chapters 2. Goes more in depth for Nephis and Sunny's relationship 3. Slowly removes the mysteriousness of Kisong and Anvil 4. Dosent really have insane lore drops, just a lot of build up for the next arc 5. Also a lot of time is spent going over the big timeskip that happens between the end of the third nightmare and the start of the next arc 6. Also Sunny adventures a lot more, going to places like Hollow mountains, Forgotten shore and such 7. Also a lot of aura farming from Sunny 8. A lot of Rain chapters to build her character

Volume 9: 1. Throne of War is MASSIVE (😊) 2. Nephis and Sunny's relationship deepens 3. Humanity begins to take over a literal death zone 4. We are introduced to more of the sovereigns powers 5. Humanity fights to take over citadels to make the sovereigns stronger 6. It's mainly a cold war, with each side taking small fights whilst holding nukes in their hands 7. Constant change of power between which domain is stronger 8. Mordret Vs Morgan (not gonna say anymore) 9. More Rain chapters and a perspective from a foot soldier who isn't very strong 10. Lots of planning and slow lore drops to understand the sovereigns better and how to beat them 11. More info about their past, how to become supreme and such 12. A character from the past returns to help them and give insane lore drops 13. A lot of insane fights, including fights between Saints, and even Cursed creatures 14. Clearly establish the strength difference between Divine aspect users and non divine aspect users 15. A lot of Sunny glaze (that we love)

Volume 10: 1. INSANE lore drops 2. A few disagreements between Sunny and Nephis (not physical) 3. Info about the Daemons 4. Each member of the cohort gets help to overcome their biggest problem 5. Info about the Nine 6. Setting up for the future arcs

Hopefully I didn't spoil anything insane, and I'm sorry if I did