Patch Available - KMST 1.2.494

From what I saw in the tutorial, I'm guessing that Luminous may need something to spark the sealing process in which it may requires a life to do the deed and Eunwol takes one for the team. Which would mean those blue sparkles he shoots to the beacons is his life essence. It could be a side effect to the sealing or a last ditch effort made by the Black Mage.

 Spoiler

Eun Wol said they needed Luminous's light magic after he offered to be the sacrifice. Freud also offered, but Eun declined it because of Freud's condition.