For what I understood, it seems we get a proper AoE combo.
We see Verthunder+Impact then three times Enchanted Moulinet, which gives three "red charges". Then, we see the red mage use Impact on a shorter cast then this upgraded version of Verthunder.
It seems these charges allow you to use upgraded spells. Meaning you can potentially go to your Single Target spell combo after three moulinets, or go to your AoE combo after the Riposte, Zwerchau, Redoublement.