It's been a week now, and I have been cleaning the house when not cultivating or practicing with the sword, after a brief look at the cultivation manual I discovered what happened with the zombie.
That transparent orb was a soul, and from its feel and coloring it's clear that it has been decayed beyond what a human soul can sustain, if it didn't enter the crystal it would have dispersed moments after the zombie truly died.
Now I know what the crystal actually is, it is a Focus, a channeling tool for mana, which can be used to perform various techniques, but it can't be used to its full potential until I am at the Soul Refinement realm.
The cultivation manual claims that the sword and the crystal are spiritual artifacts of a very high grade, as only a powerful spiritual artifact would be soul bound, the sword, like the crystal, cant be used to its full potential until I advance to the Soul Refinement realm.
What the crystal did reminded me of the third way of fast cultivation that doesn't require sunlight or fire, and that is the absorption of souls.
There are two ways I could do that, first is directly absorbing the soul, which is suicide if done before advancing way past the Soul Refinement realm, and the second is letting the soul disperse close to me to temporarily increase the density of mana in my surroundings.
The second choice is horribly inefficient but I can't accomplish the first method as I am now, these two methods are considered 'evil' by righteous cultivators, but why should I care about some 'cultivators' that don't even know I exist?
+++
I prepared to cultivate in the good bedroom, in front of an open window so that the weak sunlight reaches me, even if weak it will provide a small boost to my cultivation speed.
The past week I had advanced to the 2nd-level and then the 3rd-level Body Refinement realm, my fast speed is due to the ley line nexus below the house that provides this location with ample mana, and in my opinion, my talent in cultivation that is quite good too.
To advance in the Body Refinement realm the best method is to do a cycle of exercise and cultivation without stopping in between, this way the mana in the body is easier to move around; for that reason, I have been practicing sword techniques contained in the combat manual, as of right now I feel like I could take a group of zombies by myself.
This time I will be using the soul of that zombie, if it's worth it I will go and hunt more zombies, if not I will remain inside the walls and cultivate until I can collapse a building with a swing of my sword.
I summoned the crystal and let it float around me while I set my mindset for cultivation, when I was ready I willed the crystal to release the soul of the zombie, the soul came out of the crystal and started to dissipate at a visible rate.
In seconds the soul had completely dissipated and the density of mana around me had increased noticeably, it is worth it then to go hunt more zombies; I began cultivating so I don't waste the increased mana density in the room.
+++
After the last cultivation session, I advanced to the 4th level of the Body Refinement realm, at this point I am clearly stronger than a normal human, with an unnatural strength and durability only comparable with someone in power armor or a device similar to that.
My muscles have become more defined and my reflexes and instincts have improved dramatically compared to before, if this is the power of a 4th-level Body Refinement cultivator then I can't even fathom how powerful a 9th-level Body Refinement cultivator will be.
The cultivation manual mentioned that bloodlines affect the rate and effects of cultivation, with stronger bloodlines having greater effects, for example, a being of a bloodline with an affinity for darkness is going to have a hard time cultivating with my cultivation manual, which has an affinity of fire and light among several others.
But that's rambling, what is important is that I decided that I will go and hunt as many zombies as I can without going too far from my house, I'm not suicidal, yet.
+++
I swung my sword, killing an undead with a single swing to the head, as another zombie came out of a dilapidated building to my right, I only came out of the walls minutes before and already multiple zombies are converging in my position, I have killed 5 and stored their souls in the crystal but they keep coming, at least only one by one.
I don't feel nervous about the zombies anymore, dodging them is easier than stealing candy from a baby, I sidestepped the clumsy charge from the new zombie as I separated his head from his body.
"This is unbelievably easy, and I thought I might die, how cowardly of me to think such things..." I muttered with a frown as another zombie came out of the same building as the last one.
I didn't even blink as its head flew off its body and another soul entered the crystal.
I was about to return home and start cultivating when a sound surprised me, a animalistic roar shook the ground as heavy stomps were heard from inside the building in front of me, where the last two zombies came out.
I only had time to jump back and get into a stance as a monster of a zombie crushed the wall and stomped towards me, it looked as if someone had combined a human with a gorilla and turned it into a zombie, taller than me with muscles that looked like they could bend steel, this is not a normal zombie in any way.
"I just had to talk... fuck" I cursed and dashed to the side as the monster zombie grabbed a large rock and threw it at where I was moments ago.
"I hope my training was worth it," I thought out loud as I charged the zombie, dashing side to side as the undead threw anything it could get its hands in my direction.
When I was close enough I slashed at its legs, the zombie didn't manage to evade my sword and I cut its legs off, with the zombie landing on the ground with a loud crashing sound after the legs and the body separated.
I prepared for the finishing blow when the zombie used its powerful arms to jump toward me, I only just managed to evade its bulk as I slashed, taking the right arm of its shoulder, the zombie crashed into a rusted car after missing me, denting it severely and getting stuck in this wreckage.
The zombie tried to get out of its spot but I didn't let it live more as I cut its remaining arm, now limbless the zombie tried biting me, but that was completely unsuccessful as I was too far away.
"That... was an experience to remember," I said with finality as I slashed and cut off the head of the zombie, this time a much larger soul came out of the zombie, ten to twelve times the size of a normal zombie soul.
I sighed and returned home, I will not be tempting fate anymore.
At least I got a bunch of souls, this will greatly speed up my cultivation.