With a short side-ponytail, Kanao happened to be as tall as Nezuko with deep violet eyes and a little unusual demon-slaying uniform. Instead of pants, Kanao wore a black, pleated skirt, similar to Mitsuri's, and white, knee-high boots while a pure white cloak tied into a knot around her left shoulder. 

Just like Aoi proclaimed, Kanao remained silent the entire time as Nik observed her from to toe before nodding and taking a step back.

"With Rei and Aoi already tired, let's start the sparring with you. You can use your breathing technique.

It won't be a problem, right?"

Nik turned his heels and walked towards the stack of wooden swords and picked two from the large stack and then made his way towards Kanao, stretching his arm and passing one of the two wooden swords. Taking the sword silently, Kanao matched Nik's gaze once again.

Rei's eyes, meanwhile, instantly grew stern and carefully observed each of Kanao's body's movement. Even though Rei had managed to cultivate a crimson nichirin blade said to have extremely destructive property against demons and even got trained by the Cultivator of Fire and the Fire Pillar personally, she still fell short to the title— Successor— since she still hadn't managed to achieve the Continuous Focus Breathing Technique.

Unlike Rei, Kanao, on the other hand, had already achieved this feat. Just like Shinobu, Kanao was stuck with slightly weaker physique, but her talents in swordplay monstrous.

"You should at least speak a few words to introduce yourself if it is just to honour your opponent." Nik's sudden words attracted a startled reaction from Kanao who tilted her head in puzzlement as Nik brandished the wooden sword.

Instantly, Kanao's eyes grew wide and her body bent back till her knees while an audible sound of wind echoed within the dojo.

She avoided a simple wind attack.

"You saw it, didn't you?"

Kanao felt her body shudder as the soft whisper was too close to her. The moment she turned her head in, Kanao's eyes grew wide in surprise while her pupils reflected the edge of the wooden blade right in front of the middle of her brows, almost touching her.

"You have pretty eyes, Kanao."

Nik smiled and retracted his blade, once again, attracting a strange expression from Kanao. Smiling, Nik looked at the somewhat dumbfounded Rei and Aoi for a moment then turned his gaze towards Kanao, observing the single droplet of sweat finally dripping down her chin.

"Your reaction time is better than most, and I dare say that it has already surpassed many pillars' reaction time. 

So, we will develop your flexibility a little more to go well with your reaction time."

With a turn on his heels, Nik then pointed at the duo and smiled, "And enough rest for you two. Now get up and start focusing on your breathing techniques.

Aoi, you will spar with Kanao for three minutes with your breathing technique activated, meanwhile, I'll train Rei."

Usually, three minutes would have been nothing for a usual demon slayer well-versed with the breathing technique, but with her body already exhausted, it would be hard to stand till the appointed duration. Even Nik knew this for he went through the same thing that Rei and Aoi are going through. Training required a lot of time and to gain some obvious results, it may take even longer. And while an apocalyptic even hung above the world's neck, Nik simply couldn't dampen the motivation of the beautiful ladies willing to grow stronger.

Standing up, Rei gazed at Nik for quite a long time as she still seemed to feel his lecherous hands over her waist and the earlier interaction with Shinobu alongside the fact that Tanjiro confessed that Nik had Saeko's and Shinobu's scent on him yesterday with the scent of a few others lingering, it wasn't hard to understand the type of youth Nik was.

And Rei felt that is was only right. Instead of finding THE perfect gentleman with a deep-rooted, hidden twisted fetish, it was easier to understand a womaniser like Nik. And his earlier actions were plain implications of his objectives that he never once hid away from others.

"Your hands must stay above my waist during the spar."

Understanding was one thing but accepting another. There was no way Rei would just let a scoundrel touch her so casually, even if he is a pillar. Society has never been easy on girls, especially an orphan like her. The sternness of Rei's eyes only pulled a wide grin from Nik as his gaze roamed over Rei's voluptuous upper body.

"If that's what you want."

Nik's smile soon faded when Rei activated her breathing technique.

"Don't activate your breath of fire."

Nik broke his stance and walked towards Rei with a serious expression, his hands instantly clutching onto her right wrist and pulling her arm forward unceremoniously.

"The more we use the breathing technique, the longer the effect lasts. Aoi has just started so she can keep on using the technique with a higher frequency but shorter duration.

The opposite is true for the more experienced ones. See this?"

Nik's right index finger traced the thick vein popped out of Rei's forearm, stretching till her bicep and flicked his fingers.

"Continue the technique without any rest and your veins will be damaged."

This was something Shigure trained him in until his body accepted the entirety of the technique. Meanwhile, Rei's eyes grew dark and she instantly tugged her arm back with a snort.

"I can still activate it and I don't feel pain. Let's just spar."

"You will feel pain after the adrenaline stops rushing throughout your body. Believe me, damaged veins are hard to treat even with Hamon." Turning his head towards the silent Aoi and Kanao staring at the situation, he smiled and instructed, "You two should start ahead with the spar."

"And Rei, just come at me without your breathing technique activated."

"That won't be of any use." Rei countered with her tone laced in dissatisfaction and urgency.

"Exactly, this spar is supposed to relax the accumulated tension in your body. Rushing in for success would lead to damages that may reduce the chances of the said success."

"But—"

With a glimmer in his eyes, Nik cut Rei in between and replied with a straight face.

"There is another method, of course. Way effective than simply sparing until your body calms down before enduring the pain—"

"What is it?!"

Rei instantly burst out, once again attracting the attention of Kanao and Aoi, who were in the middle of the spar as Nik looked at them shook his head, hinting them to continue before matching Rei's glimmering pupils with a frown.

"It's a massage. But I have a feeling that you won't be willing for such a treatment. So, let's not waste our time and spar."

Nik took a step back to create a little space between them to enter their combat stance more comfortably. Well, at least, Nik entered the stance while Rei continued standing without moving a single inch, her eyes focused on Nik's face with a troubled look on her face.

"W-what kind of massage?"

With the fish reeled in, the fisherman Incubus wouldn't be damned if he ruined the entire bait with a smug grin. Reigning in on his smile, Nik stood straight once again and spoke softly.

"We should discuss this somewhere else... if that is what you truly want."