From his safe observation spot, Rei noticed that Isshiki suddenly changed his mind about fighting Kaguya and started running in his direction. This made him incredulously raise his eyebrow at the sudden twist but it also made him feel inwardly annoyed.

Rei had many observation seals all around the dimension that worked similarly to Hiruzen's spying crystal ball so he was really sitting on a small couch he had stuffed in a storage scroll while eating popcorn as he watched the fight..

And just when he was enjoying some peace and quiet, enjoying a good show... because seeing Kaguya and Isshiki fight was like a scene from a bonafide apocalyptic movie... the Otsutsuki dude simply had to ruin all the fun for him.

Still, Rei was too lazy to deign Isshiki's mad charge at him with a proper reaction and he just kept leisurely lounging on his comfy couch.

Naturally, inwardly he was prepared to instantly take action in the abysmal off-chance that Isshiki had some hidden ace up his sleeve but outwardly, Rei looked like a couch potato watching a boring movie, probably making Isshiki even more pissed as he cocked his fist back and was about to send a punch at him.

A loud clang could be heard all over the surroundings as Isshiki's advance was stopped by some invisible barrier just three meters in front of Rei. He completely didn't notice it and crashed into it face-first, getting rebounded back by his own momentum without the barrier even budging.

Rei amusedly chuckled, the sight reminding him too much of those careless kids in supermarkets that run into a closed glass door and fall on their ass because they are too distracted with their new toy.

Isshiki instantly stood up, shaking off the impact and narrowed his eyes. He still could not see the wall between them but now he knew it was there. Gripping his fist hard, Isshiki started to madly punch in front of him, desperately hitting the wall as if possessed.

Rei appraisingly watched as the Otsutsuki tried to get to him, relishing in his growing frustration and despair. Seeing that previously arrogant face finally realize just how screwed he was... it was simply priceless.

Rei wasn't in any hurry to stop Isshiki either. The man was willingly letting Rei test his anti-Otsutsuki sealing arts so why would Rei complain?

At least he didn't need to hear the constant complaining and whining of Kaguya when he managed to rope her into this kind of activity.

The angry snarl of Isshiki was music to the ears compared to that.Unfortunately for Isshiki, he didn't have a snowball chance in hell to breach Rei's protections. Rei might appear to be 'there', but he was really not.

Similarly to Obito's Kamui or Madara's Limbo techniques, Rei was in a different pocket space. This pocket space was simply close enough to his dimension that he was visually present but he was not really there.

Isshiki tried to move around the barrier and find a weak spot too but it was useless.

What he was hitting was not a barrier at all. It was the edge of the dimension itself. It was the place in which the pocket space where Rei was hiding and his dimension were meeting. The 'rift' between them was held open by Rei's seals since it was unnatural for the dimensions to be open and only Rei's seals were keeping it open.

But the kicker was that despite this the dimension being 'open', the spatial edge was nigh impenetrable, hence why Rei used it as a defensive means.

To reach Rei with his attacks, Isshiki would need something capable of breaching space itself. Technique or ability... but physical strength was not good enough.

The guy could be capable of busting a country with a punch or destroying a chunk of moon but he would still be unable to breach space.

The simplest comparison was the water walking technique. It didn't matter how many times one punched the tree, he would not be able to walk on it. To walk on it, one had to use specific techniques to get the desired results.

Rei had fun watching Isshiki in his berserk state, putting his all into punching and kicking the edge of the dimension, yet, not causing it to even slightly budge.

He was not strong enough to fight the Otsutsukis but fortunately for him, he didn't need to be. The fights on this level were not solely decided by brawn. It was just that nobody gave the Otsutsuki the memo yet.

An hour later and when Isshiki's rampage was starting to get old, Rei decided he had enough data and Isshiki was no longer needed.magic

Isshiki punched the barrier like usual, even trying to use his shrinking abilities in tandem to try if it would work... but unlike before, ink-like symbols started quickly spreading up his arm from where his fist was in contact with the 'barrier'.

​ Isshiki panicked a bit, his state of mind no longer at its best, but he still managed to pull back, only letting a small strand of symbols crawl up his arm.

With a swift and decisive slash, Isshiki quickly separated his arm from his body, deciding to regrow the entire limb rather than risk letting the seal spread all the way onto his body... but he was a second too late.

One symbol.

That's all that managed to get onto Isshiki's body, and he quickly found a small pressure descending on him, causing him to widen his eyes.

The pressure was nothing extraordinary and even a genin could probably shrug it off but it was there and Isshiki felt it. It was like an annoying fly buzzing around to his senses.

Thinking he could just blast it away with a burst of his powerful chakra, Isshiki flared his chakra... and when Kaguya saw it from her place a bit away from where she was observing him, she facepalmed.

'That... was his first and last mistake.' She dryly thought, giving Isshiki's back a deadpan look.

She would have known. After all, she fell for the same friggin' trick!

Instead of the weakened seal being blasted away with a powerful surge of the chakra, the seal started quickly feeding on Isshiki's chakra, and the more he flared it, the more the pressure on him increased.

"What the hell is this!?" Isshiki frantically exclaimed, flailing his arms as if trying to shake off the ever-increasing pressure.

From the weight capable of restraining genin it quickly grew, shooting past Jonin-level restrictions all the way to Kage level and then some...

Soon enough, when the pressure stopped growing, Isshiki was panting but he still stood upright despite the strain the seal put on his body and Rei nodded in satisfaction.

This was the limit of his seal. It didn't exactly squash Isshiki like a bug but... for now it sufficed.

Rei whipped out a small notebook and started writing his ideas for improvement, giving Isshiki a few seconds to get a breather.

When he was finished with his notes, Rei raised his head and looked at Isshiki, giving him a pleasant smile as he finally decided to answer, "That, my dear ignorant guinea pig, is one of the many, many seals I need you to try for me. Now then, shall we continue?"

Isshiki was a very driven scientist with a penchant for unconventional experiments himself. He could recognize a fellow enthusiast and his pupils constricted as he instantly knew he was in for a very long and ruthless afternoon that will definitely not end well for him.