Adventurers should always collect the magic cores of monsters they defeated. This was also written in the reference book of the prep school. Even in class, the teacher had emphasized this point.
“As expected, my mana is almost at its limit for today.” (Wendelin)
When I returned to the ship after collecting the dragon bones and the magic core, my mana already was down to the breaking point of exhaustion.
If there was another dragon, I would definitely go to the netherworld.