Arrogant as he appears, Isshiki is very cautious and secretive, capable of keeping the full scope of his abilities secret even from his allies. Isshiki muses on his poor timing, stating that if he had arrived later, he could have brought back Naruto without a futile battle, and laughs when Naruto and Sasuke instead declare the terrain allows them to fight freely against him. As Koji continued his attack while Isshiki fully unleashed his Kāma, he eventually caught Jigen off-guard, summoning a giant wall of flames. Even without having Jigen's body access more of his power, he shows tremendous speed and strength, easily kicking Naruto away, impressing the Hokage with his reaction, and effortlessly catching a punch from Kawaki when he had Kāma activated, causing Kawaki visible pain by merely lightly twisting his arm. However, after they had learned of the true nature of his abilities, Isshiki was only able to stalemate them and after escaping unscathed, realizing his foes are too powerful, he compliments his foes for fighting so well before finally completely releasing his power, progressing Jigen's Kama to the point of sprouting his horn. He can also enlarge them whenever necessary to counter armed blows from enemies.
Seeing Koji enter Sage Mode, Isshiki continued to attack Koji, casually handling his fiery assaults and overpowering him in hand-to-hand combat as he derided Koji for continuously using Fire Release and nothing else, calling him lame. At the same time, he has shown an irritable side, as when tasks fail to reach his expectations, he can lash out, as he kicked a broken tank after another setback to his plans. Effortlessly diminishing all of Koji's flame assaults, his powers now having increased to a completely different level than his already tremendous might while possessing Jigen, Isshiki even toyed with him by simply shrinking himself to Koji's shoulder to dodge his hair-manipulating jutsu and saying he could use all his power and still never able to defeat him. He notices the surroundings as the Uzumaki house and politely apologizes to Naruto for having his shoes on only to be coldly rebuffed by the Hokage, who challenged him to battle. He even toyed with Koji as soon as he was reincarnated to show the vast gap between their powers and took time to teach Koji the secrets of his techniques after decisively defeating them. Isshiki has also displayed remarkable proficiency with a large black rod to easily parry blows from Sasuke, despite his skill in kenjutsu.
Koji brushed him off and entered Take your favorite fandoms with you and never miss a beat. He has also displayed advanced mastery of Space-Time Ninjutsu compared to his fellow brethren, as he is able to apply it in combat, creating the black shrouds he uses to teleport fast enough to catch foes off-guard and teleport out of attacks at the last moment. Isshiki is also able to synchronise the Kāma he placed onto Jigen with that on Kawaki to open rifts in space between the two vessels. Slowly turning the once human Jigen into a real Ōtsutsuki. His immense devotion to his goal is such that he shows no interest to other serious matters such as Naruto, who he did not even bother to finish off upon defeating, but became interested in Boruto for also bearing Kāma, believing the boy would be like Kawaki, a "perfect Ōtsutsuki" that will further Kara's plan and having intended to take him back along with Kawaki to Kara. Unlike the other Otsutsuki, he seems to have a sense of comradery, referring to the other Inners as comrades and indicating he was willing to negotiate with Koji and Amado despite their betrayal costing him Kawaki, and is not above showing pity towards his foes, as he, albeit condescendingly, showed sympathy towards Koji for not realizing he was being made a fool by Amado and courteously and kindly asked for a last message for him to deliver to Amado.
Isshiki's power is so vast that Jigen's body, despite the various enhancements he gained to be monstrously powerful in his own right, has difficulty containing it, preventing him from using the full extent of it for long. The kama seal grows around Kawaki altering his appearance by making him grow a horn on the side of his head to Isshiki's surprise as he didn't expect Kawaki to develop so rapidly.
When unleashing more of his power through Jigen's Kāma, his chakra was such that it intimidated Sasuke into fleeing and later on unnerved both him and Naruto. At the same time, Isshiki viewed Koji as a fool himself, having been made as a sacrificial pawn, knowing that Koji would have no chance of defeating him.
Isshiki is a cruel, ruthless and pragmatic being, having completely overtook Jigen's mind and body and showing no care or respect for the body he inhabits, cursing at his limits and degrades him as a worthless vessel. Isshiki began shrinking various targets around him, forcing Koji to dodge. Isshiki is capable of making use of black rods to an even more lethal degree than the Otsutsuki and other Rinnengan users: In addition to his rods being able to uniquely drain chakra, upon using more of his power, Isshiki can instantly summon them so fast that both Sasuke and Naruto weren't able to react to it and even form them from his neck to defend himself from Sasuke's attack. Isshiki é arrogante, pragmático e rude.
Through scientific aid, Isshiki was able to transfer his Kāma to a more suitable vessel, albeit with a very low success rate, with Kawaki alone out of fifteen children to have survived the process.
Casually dodging Koji turning his hair into needles, Isshiki commented on how tremendous his powers are but also revealed that Jigen's body would die in 2-3 days due to being unable to withstand it and cursed Amado as he had lost Kawaki's Kama but ridiculed Koji for still not understanding that Amado had been using him all along and had never intended him to survive the battle, knowing fully well only the Hokage and Sasuke can possibly defeat him, correctly knowing Amado sought refuge in Konoha, and derided him for believing himself to be a shinobi while in truth he was a mere sacrificial pawn.