Puzzle

Asher then just got ready for class, and as he was heading towards the cafeteria, he thought to himself, 'I lost 30 vessels in just a matter of an hour, and now I don't even have 100 master-rank vessels left. As expected, grandmasters are a league above masters in fighting power. Even if I use 'Nothing' to fight against them, I am still too weak to face them unless I have an advantage in numbers. The only reason I won against the necromancer was because my power happened to be exactly his weakness — otherwise, I might have lost.'