People were quite surprised when Nintendo released the trailer for Super Smash Bros. Ultimate World of Light which teased the game's single-player mode "Spirits." While I wouldn't say anybody died, the trailer certainly racked up a large bodycount with nearly every Nintendo character in Smash getting blasted by beams of light. The only survivor of course was Kirby.
In a column Famitsu, Smash Bros. Ultimate director Masahiro Sakurai gave a canonical reason as to why Kirby, out of all the characters in Smash Bros. Ultimate, was the only character to "survive" the encounter with the destroyer of Nintendo IP. According to Sakurai the decision to have Kirby survive required careful consideration of all the characters' skill sets and abilities.
"We needed a solid, convincing reason for why said character could outrun Galeem. All fighters possessing "normal" abilities were immediately disqualified. Given that its assault enveloped the ends of the galaxy, only a vehicle that could defy the laws of physics would work. Even short-distance teleportation wouldn't be enough."
This narrowed the field down from the sizable Smash Bros. Ultimate cast to characters with extraordinary travel capabilities. They'd also need an ability that could bend the laws of nature, so it'd have to be a character with access to some kind of outer worldly ability or transportation. Hence the field was narrowed to three.
"Some of you may have forgotten but Kirby's Warp Star has been able to, y'know, warp since his very first game. That alone made him a pretty solid contender. The only other two fighters that could have survived would have been Bayonetta or Palutena. That said, Bayonetta's enemies from Purgatorio (a hellish other world) were turned into Spirits, so it wouldn't have made sense for her to escape. Other divine beings like Hades were also turned into Spirits, so there was no way Palutena could have survived, too."
The trailer is actually an official introduction to Smash Bros. Ultimate's Spirit mode as Kirby is the starting character for Spirits. Players must traverse Spirits and complete challenges and defeat possessed versions of the Smash Bros. Ultimate cast to free them from Galeem. Gameplay-wise Sakurai said that Kirby was a good choice as the starting character as the first fighter needed to be "simple and easy to use."
You can read our preview of Super Smash Bros. Ultimate Spirits here or our Smash Bros. Ultimate character guide. Super Smash Bros. Ultimate is coming out for the Nintendo Switch on December 7, though it suffered a severe leak recently.