WARNING: The following contains spoilers for Chapter #55, “Legacy,” of Boruto: Naruto Next Generations by Masashi Kishimoto, Mikio Ikemoto, Mari Morimoto and Snir Aharon, now available in English from Viz Media.
Chapter #55 of the Boruto flips the manga on its head with Naruto losing Kurama and Sasuke realizing his Rinnegan's gone forever. But there's even more to unpack in the bombshell reveal that, whilst Isshiki Ōtsutsuki was dead, he left a successor in Code and a power source in his White Karma mark.
Isshiki wants the teen to finish his plan, feed Kawaki or Boruto to the God Tree, conquer Earth and then travel to other planets to bleed them dry of chakra too. However, as much as he wants this mark to turn Code into the ultimate god, this stunning gift might mean bad news for the Ōtsutsuki clan, as well as for readers who wanted to see more of the aliens.
Boruto has never revealed the full story on why these particular soldiers -- Kaguya, Momoshiki, Isshiki, Kinshiki and Urashiki -- were sent to Earth, nor has it revealed what's up with the royal family. Their entire history and kingdom is a mystery, so when Isshiki appeared in the series, many expected him to reveal the full truth. At the very least, it seemed like other aliens might come to find out why Isshiki, Kaguya and the others failed, as there did seem to be a civil war back home. However, Isshiki's actions hint that his home might not exist anymore.
Seeing as Isshiki wants Code to go across the galaxy, consuming and becoming the ultimate Ōtsutsuki god, one has to wonder why would he expect no other clan members to be doing this too. If Code meets up with other aliens, he'd likely be destroyed, as he's an alien-human hybrid as opposed to a pureblood alien. However, Isshiki's words make it seem like there's no chance of Code encountering other clan members out in space.
If Code is the only person Isshiki has to carry on his legacy, this implies that the entire clan is dead. It could be why he was betrayed by Kaguya, as they were looking to see who'd be the final member. If Kaguya got the ultimate power by not losing to Sasuke and Naruto, she would have been able to kill all other invaders from her species. It feels like these are the remnants of a dying race, all rushing to be the last survivor. This would also explain why Isshiki doesn't mind Boruto being fed to the tree because this would mean Momoshiki can't be resurrected. This way, Isshiki gets to be the uncontested survivor through Code.
It's not just about Isshiki living vicariously, but about ruling the entire cosmos, taking pride that no other Ōtsutsuki soldiers can achieve this amazing feat of interplanetary domination. Had there been others, Isshiki would have warned Code of rivals and aliens seeking this birthright. But instead, Code now has the keys to the kingdom, which explains why Isshiki handed the baton off to him like a 'son.'