Nezuko is the very first demon to walk under sunlight. Muzan found out about her after witnessing her unique ability to resist sunlight which is one of the traits of demons.

His informants and observers throughout the various battles involving Tanjiro and Nezuko made him depict or pique his interest and desire to capture her after witnessing her, which is a treat.

Nezuko’s Unique Traits That Caught Muzan’s Attention

Resistance. To light, Mystical is not just like any other ordinary demon, but she shares a close relationship with one of our main protagonists, Tanjiro.

Nezuko’s ability to walk under sunlight and her connection with Tanjiro, a demon slayer, made her catch Muzan’s attention and become a potential threat to his plans.

1. Resistance to Sunlight: 

After undergoing a series of transformations, Nezuko’s ability to withstand sunlight caught the attention of Muzan because Muzan’s initial goal was to find a way to overcome this challenge of sunlight because he was still a demon that could become prone to sunlight.

Therefore, realizing Nezuko’s ability to withstand it made her his foundational target to get that resistance he needed.

Because over the years of Muzan’s work and development as a demon, he has been searching and constantly looking for ways he could develop himself to become resistant to sunlight.

2. Human Emotions and Self-Control: 

Nezuko is one of the few demons who can resist the urge to kill and consume humans. Therefore, she retains her human emotions and consciousness throughout the series.

Despite her demonic transformation, which was intriguing and entertaining, her ability to maintain her humanity during the time makes her a valuable study object or subject to muse.

3. Growth Without Consumption: 

Initially, demons repent upon human flesh consumption to increase their strength and regenerate their powers. And normally a demon’s power is inspired by the amount of humans they consume.

But, Nezuko was one of the few characters who grew stronger without even having to touch any human flesh to enhance her power.

Therefore, Muzan’s attention was directed towards this girl due to her special capabilities. He had human killing urges, and this was crucial for his plans to enhance the demonic army that he was hoping to create.

The Impact of Nezuko’s Powers on Muzan’s Plans

• Potential for Immunity Against the Sun: Nezuko’s ability to resist sunlight was Muzan’s main goal because he needed to harness Nezuko’s power to create more sun-resistant demonic breeds, which would be a stepping stone for him to take the human world.
• Disruption of Control: Nezuk’s presence influences Muzan’s incitement, and he knows that if he doesn’t control it, he might be able to get a bit of disobedience and rebellion amongst his ranks.

Also, Nezuko’s ability inspires other demons to defy Muzan’s reign and feature his existence. Therefore, he needs to attain Nezuko’s abilities to avoid this disruption.

Muzan’s Network: How Information Reaches the Demon King

• Spy Network: Muzan maintains a series of networks involving spies and demons’ subordinates who report directly to him, providing him with intelligence. He also contributes to the Demon Slayer crew.
• Direct Surveillance: He has shape-shifting capabilities that allow him to hide his identity and take the initiative to observe and interact with his interests with ease without the need him be a threat. This allows him to plan his strategies better and more efficiently.
• Use of Curses and Compulsion: Muzan uses curses and compulsion to control and extract information from other demons. This ensures loyalty. But at the same time, he Instills fear in his subordinates to have control over them so that they can keep themselves updated about unique powers likeNezuko’s powers.

Therefore, we would say that Muzan discovered Nezuko after he learned about her sun-resistant abilities from his informants.