WARNING: The following contains spoilers for Boruto: Naruto Next Generations Episode 218, "Partner," now streaming on Crunchyroll.
In the Boruto anime, Naruto found himself having to power up like never before to protect his son, as well as Sasuke and Kawaki. Isshiki has finally emerged in his Ōtsutsuki form, causing the Hokage to activate his Baryon Mode and attain godlike levels of chakra in a secret dimension. Unfortunately, despite the Konoha leader's efforts, the series takes a major casualty by killing off its most powerful hero.
This is none other than the Nine Tails Demon Fox, Kurama. Ironically, the most senior of the Tailed Beasts debuted in the first Naruto episode in 2002. 19 years later, on the very same day, the mystical being officially dies as he sacrifices himself for his human host.
It's a heartbreaking death, and what makes it even more sentimental is he tricked Naruto, all to preserve the person he's been embedded within for decades. This is due to the Baryon Mode pact where Kurama told Naruto that once Isshiki's body expired, the Hokage's energy would be depleted too and the leader would die. With Isshiki now being crushed to dust, Naruto enters the astral plane where he's ready to accept moving to the afterlife, but the fox admits he misled Naruto.
Kurama is actually the one who'll disappear, which breaks the rules of when a vessel for a Tailed Beast becomes separated. Usually the host dies but in the Baryon pact, Kurama will dissipate into nothingness, leaving the Hokage with the memories of all they shared together. It gets super emotional, reminding us of when Naruto met his mother, Kushina, and father, Minato, because as much as Kurama is a sibling, he's also been a parent.
Kurama was implanted by Minato as only Naruto's blood could quell his rage, and in time, Naruto would see the humanity in these beasts, not wanting to weaponize them. Kurama admits this is what changed his perspective and felt whole knowing Naruto cared for them, called them by name and showed them the love the Sage of the Six Paths did when he kept them as family, not pets.
Now at this stage in Boruto, Kurama had to deceive Naruto because he knows the Hokage would not have activated Baryon Mode if he'd known the fox would perish. It's a brutal lie of omission but ultimately, one that saves the day as it weakened Isshiki in battle for Kawaki to kill him. Still, it's not easy to stomach as Kurama's power surpasses so many -- even Sasuke, Obito, Itachi, Madara and aliens like Kaguya and Momoshiki.
He's been helping Naruto become this perfect liberator for so long, and it's why Naruto begs him to stay and even considers dying with him as he knows Konoha will be in great hands. He just doesn't want Kurama to be alone but as the fox bids him goodbye with their signature fist-bump, Kurama admits he's happy to have known Naruto's warmth. He remembers all the versions of the boy who became a man under his watch, and passes in a happy, virtuous death to end a very stoic era in the Naruto/Boruto franchise.