If it were just a matter of HP recovery, that wouldn't be too much of an issue; they could simply continue the fight and defeat the boss.
The real problem was that the wound on the boss's throat had started to heal, which meant it could resume its ultrasonic attacks.
The previous sonic assault had already left them disoriented and in a poor emotional state, even drastically reducing their mind power.
Another such attack now would not be so easily handled.
The boss was now on alert and wouldn't likely allow John another direct attack.
No matter what, they needed to finish it off quickly.
"How much MP do you have left?" John asked.
He had finally pinpointed the most vexing aspect of this boss: if the sonic attacks were manageable, then Blood Absorption was truly the worst.
Just as they were about to deplete the boss's HP, it had replenished itself, a situation that could frustrate anyone to the point of explosion.