"Hydra's Debut Stage" 

The low-level Valkyries really didn't need to retreat like that. 

Just ask the mid-level Valkyries to extinguish the Ring of Fire that was protecting the two creatures and the low-level Valkyries could absolutely eliminate both the Centaurs and Harpies. 

But how come...the low-level Valkyries looked as if they had finished their job and retreated to empty the stage for the mid-level Valkyries?

What Code-L didn't know is that, even among Valkyries, there were still rank suppression and other military merits whatsoever.

Once the low-level Valkyries were almost defeated, it meant their time was up to create military merits for themselves, and it was the mid-level Valkyries' turn to accumulate military merits. 

Unlike celestials in this world, who had a little amount of holy light that they would only get from a blessing, the Valkyries had a specific way to strengthen their holy light.