"No matter how big a creature is, their weaknesses generally remain the same. The heart. The brain. Sometimes a few other organs too. You do enough damage to these, and no matter the size, they'd drop all the same.

Getting to those organs is the hard part, honestly." - Nakor Bersairus, former hunter and adventurer, famed as a big game hunter.

Inside the blood vessel, it was full of the thick, viscous blood, the shade of wine. Aideen held her lantern with her mouth, but even with the light it gave, she could barely see a couple meters ahead of her in the viscous fluid.

Swimming in the blood felt closer to swimming is a massive barrel of syrup rather than water, an effort that proved quite strenuous. Aideen was just glad that she had no need to breathe, which was one less worry to have.

For the most part, she had just gone with the flow, as she had made sure to choose a blood vessel where the blood appeared darker in shade. From her medical experiences, that indicated the blood had already coursed through the body, and was on its way back to the hearts and lungs for replenishment.

Aideen avoided smaller vessels that branched off the sides of the vessel she was in, and instead traced it until it joined into a larger vessel, one that could have easily fit in a fishing boat, and followed that vessel instead.

She repeated the process several times, swimming in the thick blood without knowing how much time had passed, until she finally heard the first signs that she had taken the correct path.

All around her, the blood vessel reverberated with a constant, rhythmic beat. The beat of a heart at work. She continued on her way down the blood vessel, listening and feeling as the heartbeat grew ever louder as she approached the source.

Eventually she passed from a cavernous vein into a beating, pulsing structure. The heart of the beast itself. Aideen knew she could do some serious damage there, but for that, she needed proper information first.

Fighting against the strong currents which propelled the blood, she swam and inspected the beast's heart - a massive organ easily the size of the chapel back at her hometown, if not larger - as she left no nook or cranny uninspected.

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The beast's heart seemed to be divided into six chambers, three on the side she entered, and three on the other side. The membrane and valves between each chamber were more malleable, but just as sturdy as the rest of the beast's organs, which was not unexpected.

Aideen was by no means an expert in monster biology, but her training with the Death's hand kicked in. She had previously learned the most efficient ways to topple down buildings from them, how to target the weak, load-bearing spots and pillars.

She applied that same knowledge to the beast's heart. She had forty-five vials of Dragonfire brew remaining with her, having plunged into the beast with fifty. Two she had used to escape its stomach, and three more to deal with the parasites.

The effect of the brew was most noticeable when she detonated it inside a gap in the stomach. The two she detonated on top of the organ merely carved in shallow wounds into it, a far cry from her previous results.

Meanwhile, the muscles of the heart were even tougher than the walls of the stomach. Aideen decided to go on an all or nothing gamble, to use every last vial she had on her for the task at hand, namely to cripple or kill the beast.

First she had to determine the weakest part of the beast's heart, a task that took her a long while, as she had to inspect every part of the massive organ closely, while keeping herself in place against the constant current of the blood flow.

She determined the middle chamber to be the ideal spot after some thought. The chamber was smaller, which would allow the force of the blast to be more concentrated, hopefully enough to destroy the organ.

Diligently, Aideen brought out her weapon, and using its blade like a pickaxe, she started to work on the walls of the middle chamber of the beast's heart. She made a cluster of holes just large enough to fit a vial in the center wall which divided the heart into two sections, enough to fit a good fifteen vials in.

Then she worked around, creating a hole every few meters, in a line that ringed the chamber. By the time she was done there were a multitude of small holes on the walls of the chamber, as well as a few on the floor which led towards where the valve to the next chamber was.

Aideen carefully stuffed a vial into each hole, taking great care not to break them prematurely as she went around. She placed vials into the holes on the floor of the chamber last, and looked at the valve nearby.

With a determined look on her face, Aideen inspected her work once more to be sure, then she allowed the current to wash her away into the next chamber through the valve below.

Once in the next chamber, she swam back up towards the valve, and tried to stay close to it even against the blood flow. Even with her prodigious mana and healing capability, Aideen was not confident she would be able to preserve her physical body had she been in the chamber when the explosion went off.

So instead, she chose to trigger it from.the next chamber. She carefully dug holes for her toes to grip on near the valve, then brought out the last vial from her storage ring. She kept the hand with the ring tucked behind her back, shielding it with her body.

If she lost the ring, she definitely was not looking forward to scouring every centimeter of the beast's carcass to look for it, so she tried her best to keep it safe behind her.

Carefully, she pushed the last vial into the valve. It was close to the nearest vial she had buried in a hole, not three meters away, hopefully close enough for the explosion to trigger a chain reaction. The valve closed on the vial just as Aideen let go, crushing the glass between the walls of muscle.

The next thing she knew, the world had gone white.