The Boruto series has created a wide range of interesting villains that played an important role in the progression of the plot. The Otsutsuki clan is one of the most feared groups because of their chakra reserves and their combat abilities. They are literal Gods in comparison to Shionbis and Kunoichis. Among the Otsutsuki clan members, there was a cut above the rest. This character is none other than Isshiki Otsutsuki. However, the question that most fans have is this: Who killed Issiki Otsutsuki in Boruto?
Naruto and Kawaki’s combined efforts killed Isshiki Otsutsuki in the Boruto series. Isshiki was an exceptionally powerful being who also led the Kara. He wished to use Kawaki’s body as a vessel and become the most powerful being in the world. However, his ambitions were put to rest all thanks to the Hokage’s efforts. This is also when Boruto fans witnessed Naruto’s most powerful transformation of all time.

The transformation in question was called Baryon Mode. The Baryon Mode quite literally replicated the effects of nuclear fusion. This is a process in which two light nuclei forcibly fuse to create a much heavier nucleus, and this releases massive amounts of energy. A similar concept was employed in the anime series when Kurama and Naruto decided to fuse their chakra in this manner.
Isshiki Otsutsuki outclassed everyone on the battlefield. The Hokage was forced to use his trump card. He was ready to sacrifice his life since the transformation rapidly drains the life force. Naruto and Kurama’s chakras were forcibly fused in a fashion similar to nuclear fusion, which drastically increased his overall combat abilities. In this transformation, Naruto was able to defeat Isshiki with little to no effort.

Naruto didn’t approach Isshiki with the intention to kill him. He just continued to land attacks, and the intention was to drain away his life force. Kurama instructed him to land hits and not focus on the intensity. As Naruto kept landing hits on Isshiki Otsutsuki, his lifespan shortened considerably.
It finally reached a point where Isshiki only had a few minutes left. Moments before his death, he attempted to implant the Karma seal onto Kawaki. However, he failed to do so because Kawaki used a Shadow Clone and hid from Isshiki. Eventually, Isshiki died and turned into a pile of ashes.
Boruto: What happened after Isshiki Otsutsuki’s death?

The follow-up question that most fans have is this: Who is the next big threat? Momoshiki Otsutsuki has terrorized the entire village during his time. He is a lot more methodical, manipulative, and willing to go to extreme lengths to achieve his goals. In fact, he succeeded in obtaining Boruto as his vessel in the manga. Thanks to his efforts, he is now a full-fledged Otsutsuki.
Fans are unable to figure out what his true goals are. However, he has emerged from hiding in the Two Blue Vortex installment of the manga series. He has an arrangement with his vessel since the protagonist has requested his powers against Jura. If this is the case, then fans should brace themselves as his true intentions will be revealed soon.
Isshiki Otsutsuki was an incredibly powerful character in the Boruto series. However, he was killed by Naruto and Kawaki, with the former playing the biggest role in his death. Naruto’s Baryon Mode was pivotal in destroying Isshiki in the manga, and Kawaki’s decision to hide during Isshiki’s final moments was crucial.