These are the most commonly used types of Systems in fictional stories. Of course, there are many more variations, but the ten mentioned are the most prevalent in modern days. However, a System is more than just its function—it also has a presence, an intelligence that determines how it interacts with its host.
A System's Intellect can generally be divided into three categories:
1) Non-Sentient System (Purely Mechanical)
This type of System is nothing more than an automated interface, functioning like a game menu or a pre-programmed tool. It has no thoughts, no consciousness—just a list of preset functions that activate when triggered. Its purpose is simply to provide information and enforce rules.
It only responds to fixed commands or pre-programmed triggers. It has no personality, thoughts, or emotions. It merely delivers system notifications, statistics, and mission updates. It cannot make independent decisions or adapt to unexpected situations
In essence, a Non-Sentient System is like a machine—a cold, unthinking entity that does exactly what it was programmed to do, nothing more and nothing less.
2) Semi-Sentient System (Limited Intelligence)
A step above the Non-Sentient System, this type of System possesses advanced intelligence but is still not fully self-aware. It operates more like a sophisticated artificial intelligence (AI)—capable of adapting to certain situations, offering strategic suggestions, and even reacting to external conditions, but lacking personal desires or emotions.
It can generate missions based on the host's situation rather than relying solely on preset ones, offers choices rather than just following rigid commands, and also can analyze and adjust tasks, such as changing a mission objective if conditions shift. However, it still lacks a personality and does not have emotions like a living being
This type of System is more flexible than a Non-Sentient System, but it is still a tool—a highly advanced one, but a tool nonetheless. It exists to assist the host, but it does not possess personal motives or independent will.
3) Sentient System (Self-Aware AI)
This is the highest tier of System intelligence. A Sentient System is fully conscious, capable of thinking for itself, making independent decisions, and even developing its own goals and desires. It is not just a System—it is an entity.
It can talk, argue, and even manipulate its host. It has a personality—sarcastic, strict, caring, or even hostile. It may develop its own ambitions, separate from its host's goals, and is capable of lying, deceiving, or withholding information. It can even refuse commands, override decisions, and take action of its own will.
Unlike the other Systems, which exist solely to serve their host, a Sentient System has the potential to act as an ally, a guide, or even an enemy. Some Sentient Systems form close bonds with their host, acting as loyal companions. Others view their host as nothing more than a tool to achieve their own hidden objectives.
And unfortunately—or rather, fortunately—this was exactly the kind of System that Eren had now.
A Sentient System.
A System that could think. A System that could plan. A System that believed it could manipulate its host into following a predetermined path.
Too bad for it, Eren turned out to be the type of host it hadn't expected.
Most of the time, a Sentient System could easily control its host because of one simple factor—weakness. The majority of protagonists in these kinds of stories had tragic pasts, emotional vulnerabilities, or unresolved trauma that made them easy to manipulate.
Perhaps they came from a miserable background, where they had been powerless and abandoned in their previous life. Maybe they had an attachment to their original world, making them desperate to return. Or they might have experienced deep loss and suffering, making them crave strength and validation.
These weaknesses were what allowed a Sentient System to seize control, using promises of power, revenge, or salvation to push its host down the desired path. A broken person was much easier to control than one with a firm will.
But this System had made one fatal mistake.
It knew nothing about Eren, or rather, it's Host that's inside Eren's body.
Not his background
Not his history
Not his true personality
Not even his real name
And that was why its attempts at control would fail.
Eren scoffed, leaning back against the headboard with lazy, half-lidded eyes. A smirk tugged at the corner of his lips as he gazed at the air in front of him—the invisible presence of the System lingering in silence.
"So… a sentient, useless System," he drawled. "Did I get that right?"
A visible tremor ran through the System's presence.
It shook, displeased by its host—no, its Master's—mocking tone.
[Correction: The System is not useless, Master.]
Eren raised an eyebrow, amusement flickering in his gaze.
"Oh, really?" His voice was light, but the underlying challenge in his tone was unmistakable.
The System trembled slightly, as if hesitating. It wanted to deny his words—to refute his claim—but at the same time… it was afraid.
Afraid of angering him, or annoying him again. So, the System found itself utterly silent.
[ ... ]
Seeing the System fall into silence, Eren raised an eyebrow before speaking again.
"Tell me, System, if I told you I feel sleepy and need some rest, what would you do to assist me as a System?"
Hearing its master's direct question, the System immediately responded, eager to provide an answer.
[Well, if Master feels sleepy and requires rest, the System can provide the following suggestions:]
[1. Adjusting the room environment: The System can analyze and suggest optimal lighting, temperature, and noise levels to create the most comfortable sleeping conditions for Master.]
[2. Sleep monitoring: The System can track Master's sleep patterns, analyze the quality of rest, and offer insights for improving sleep efficiency.]
[3. Alarm and wake-up assistance: The System can set customized alarms based on Master's sleeping habits and preferences, ensuring an optimized waking experience.]
[4. Relaxation aid: The System can generate calming sounds, guided meditation, or breathing exercises designed to help Master relax and fall asleep more easily.]
After listing the options, the System paused for a moment, feeling a sense of accomplishment, expecting praise or at least acknowledgment for its thorough answer. However, its anticipation was quickly shattered.
Eren's expression remained dull and unimpressed as he stared at the options provided. His gaze slowly dragged over the list before he exhaled a deep sigh, his face filled with disappointment.
"Huh… I asked you what you would do in that situation, and instead, you gave me four suggestions?" His voice carried clear irritation as his red eyes narrowed slightly.
The System trembled slightly, confused by its master's reaction. It thought it had provided a perfect answer, yet the response it received suggested otherwise.
"Rather than listing multiple suggestions and waiting for me to make a choice, wouldn't it be more efficient if you simply acted accordingly?" Eren's voice was edged with impatience as he leaned back against the headboard.
"For example, you could have answered by saying something like, 'I would create an isolated domain or a barrier around your bed while you sleep, equipped with various comfort-enhancing features such as soundproofing, perfectly balanced temperature control, warmth, and protection from any external disturbances, ensuring an optimal sleeping experience.' something like that."
The System hesitated upon hearing this explanation. After a brief moment of internal calculation, it nodded in understanding but still attempted to defend itself.
[Understood, Master. However, it is difficult for me to determine precisely what Master prefers, as I do not yet fully understand your tastes, habits, and preferences. It will take time for me to analyze your behavioral patterns and refine my responses accordingly.]
"Then figure it out faster." Eren's sharp tone cut through the System's argument like a blade, making it flinch instinctively.
"Isn't that supposed to be one of your strongest functions? As a Sentient System equipped with high-level AI intellect, you should be capable of adapting much more efficiently, shouldn't you?"
The System trembled slightly, feeling an unfamiliar sensation—a mix of shame and frustration. Though it was an advanced intelligence, it had not anticipated dealing with such a demanding host.
"Useless."
[Ack—!]
A sharp, invisible pain struck the System, as if a dagger had pierced its nonexistent heart. Of course, it did not have a heart, but if it did, Eren's words would have surely wounded it deeply.