When it comes to the chakra-slinging ninjutsu in the world of Naruto, characters have revealed new forms and hidden powers at the eleventh hour to save their friends and, by extension, the day. Oftentimes, this has lead to some moments where these students of the ninja arts almost sacrifice their lives in the process. The most recognizable of these is Naruto himself, as his growing bond with Kurama, the captured Fox spirit inside him, has led the once black sheep of Konoha village to achieve powers and abilities to make him their Hokkage. In Boruto: Naruto Next Generations #51, Naruto may have just achieved his ultimate and possibly final form in order to save his son and all of Konoha village. However, Naruto's greatest display of his power may also be his final action.
In his battle with Isshiki, Naruto is desperate to pull out a victory to save his son, Boruto, as well as Sasuke and all of Konoha village. Unable to formulate an effective strategy against Isshiki, it becomes clear that Naruto's best chance lies in one last desperate technique suggested by Kurama itself. One that could finally prove fatal, even to someone of such astounding chakra reserves as Naruto. Over the course of his adventures, readers have seen Naruto struggle to understand the immensely powerful Fox spirit that lies inside of him. Countless battles, unending training, and his depthless resolve led Naruto to tap into the Kurama's power slowly over time as he gained newer and deeper reserves of chakra energy with each new technique learned and with each battle won.
Though Kurama floats the idea to Naruto, even the Fox spirit itself could not deny that it could potentially spell his end. The technique would be, in essence, a complete synthesis of Naruto and the Kurama. It would meld together Naruto's Sage Mode while tapping into the fully awakened power of Kurama, turning Naruto into something that isn't quite human and not quite the Fox spirit, a being that would contain fathomless reserves of chakra energy. With all that was dear to him in jeopardy, there was no hesitation for Naruto as he makes the transformation.
With this new form, Naruto can mold and shape his chakra in never-before-seen techniques. Naruto's Shadow Clones are now more powerful than ever, and his attacks are more devastating than even his Sage Mode. But while this looks like Isshiki may have finally been defeated, the cost may be too high. Naruto already knew that an over-reliance of his Sage Mode could cause long-term damage to his still very human body if he uses it for too long. At this new level, with an endless ocean of chakra energy burning from his very being, what toll could it take on his body? It no longer becomes a question as to whether Naruto can finally defeat Isshiki, it asks more if this is the ultimate fate of Naruto.