When it came to the usage of Haki, it relied on the willpower and intent of each person who possessed it.
It could let them use their Haki in various ways once they awakened it, and that would let them gain a higher mastery in areas that they were able to learn on their own or through guidance.
The usage of their Haki was dependent on their physical and mental state, so it was deeply tied to their mental capability to control it and their overall vitality.
They could only use that type of Haki if they had been able to awaken it.
If they had awakened it, they would not be so skilled in using it unless they had been able to hone it in some way.
Even if they did hone their Haki, they were not guaranteed to possess Conqueror's Haki, while others would only be able to train in one type rather than training in all two or three that they could possess.
Even if they had a high mastery over Haki, they still had to use it as efficiently as possible to be able to make use of it for as long as possible for the purpose they would need it for.
That limitation of the usage of Haki would not allow them to use it all of the time without resting and recharging their physical and mental state.
That meant that even the most trained Haki user could not keep up their Haki all of the time, and that they had to have the intention to use it.
Some could use it instinctively if they were extremely skilled, but that would only usually apply when it came to certain situations, when it was demanded of them.
Sometimes instinct or some other need for survival would take over, but it would not be so useful all of the time.
Perhaps that would sometimes be the reaction of their Haki wavelengths being exposed to another and picking up on the intent behind it.
It could be very useful for survival, but it would not be so useful for the present situation.
The system could pick up on the skills of others, including whether they had Haki, along with the mastery each person had achieved, and Alyssia could sense each person who was patrolling the area using her Haki if she really wanted to do so.
Even if they possessed Observation Haki, she was still able to slip past them and go unnoticed as a result of wearing her invisibility suit that had been improved slightly.
Some people possessed exceptionally strong wills that let them achieve many great and impossible feats, that let them go beyond what should have been physically or mentally possible.
Examples were like how Whitebeard was able to live through so many wounds, old age and sickness and keep fighting so fiercely, or how Portgas D. Rouge was able to hold off giving birth to Ace and hide her pregnant state until much later through sheer willpower.
Some cases often defied common sense, but not everyone was able to achieve those types of impossible feats.
Sometimes it was just a natural part of their disposition or something that they had to learn through experience or training.
Not everyone was able to achieve those things, even if they were able to possess the right disposition to unlock Conqueror's Haki, just as they might never gain the right kind of conditions needed to unlock the other two types.
Sometimes it was just luck or fate that could lead to the right kind of opportunities and experiences needed for an awakening to happen in the first place.
After that awakening, there would still be a need to improve it from the very beginning and to keep pushing through under the right conditions needed to gain a much higher mastery over it.
None of them was able to sense her since they could not see her, and they did not have the intent to use their Haki to search their surroundings.
If they were alerted and found something strange, then perhaps it would be very different.
There were not many among those on the island who possessed Haki, but it seemed to be much higher than the average island she had been on so far.
The main difference was that the Haki possessors all seemed to belong to the same group, and none existed outside of that, as if all of the power had been built around the current ruling party.
Those who possessed Haki were paid attention to by Alyssia as she noticed how their Haki mastery varied a lot between some of them, as some had a lower mastery, while there were even those who had much stronger Haki.
It had helped that Alyssia had been working on ways to suppress her Haki to hide herself better so that her Haki would not leak out and be so easily picked up by other Haki users.
There was little need for her to use it when she had such a strong sense of smell and hearing to aid her that went along with the other senses that aided her in the present situation, like her ability to see better in the dark.
She was able to reach much further inside of the Empirica Island without alerting a single person and had even been able to avoid detection from the guards who were on duty and possessed Observation Haki.
Even if they possessed Observation Haki and were using it, the way they used it could affect how they would sense things and what they would sense.
If they were too intent on sensing one person or carrying out one task, then they could miss out on a lot more in their surroundings.
That could be proven even more by the fact that two users of advanced Observation Haki with future sight capabilities would be fighting each other and would be able to deal with the person who was in front of them, but they could be caught off guard by someone interfering.
It was the same if the attention of someone was primarily on one person the whole time, but someone was hiding covertly and would not be sensed, even if there was more than one person there that was capable of using advanced Observation Haki.
It had applied in those ways, but the type of Haki usage they mastered had that much of an impact on those things, as some would be more suited to sensing other things, like emotions or inner thoughts, while others would be able to feel the changes in others or the environment.
Each person would have their natural affinity that would be more linked to their natural talent or disposition, just like there would be those who possessed the capability to hear the voice of all things.
Her many skills related to architecture and many more of them let her make a map of the entire island by looking at it from the top of the walls.
She had done the same thing a long time ago when she visited the last time and took some time to observe everything from the sky.