Chiyu opened the Exchange Shop while on the move, selecting a suitable sensory ability.
Chiyu currently had only 1,310 Witness Points, leaving him with very few options.
He immediately disregarded sensory ninjutsu and other abilities that required learning.
Those required the system to take over his body for simulated training, and the current circumstances simply did not allow Chiyu to learn in the middle of battle.
What Chiyu needed was a sensory ability he could use immediately.
Sensory abilities that could be used directly were quite expensive in terms of Witness Points.
For example, Zenitsu Agatsuma, a Thunder Breathing user, possessed hearing far beyond that of ordinary humans, but it required a full 10,000 Witness Points.
His hearing was absolute pitch beyond absolute pitch. He could hear breathing, heartbeats, even the sound of blood flowing. If he listened carefully enough, he could even perceive what people were thinking.
Chiyu simply could not afford 10,000 Witness Points.
After searching for a while, Chiyu finally found a suitable sensory ability.
First-stage Observation Haki required exactly 1,000 Witness Points.
Observation Haki allowed one to keenly sense another person's "presence."
It could read the location and number of enemies outside one's field of vision, as well as the actions they would take in the next instant.
Observation Haki had many functions: sensing attacks, predicting an opponent's next move, sensing the strength of living beings, sensing their emotions and thoughts, and sensing the locations and numbers of objects outside one's field of vision.
Observation Haki could even foresee the future.
However, Observation Haki was closely tied to one's state of mind. It required calmness to use, and could not be used when one was emotionally agitated or had lost one's reason.
Chiyu himself was very calm, so this drawback was not a problem for him.