One of the most venerated characters in Naruto mythology is the Sage of the Six Paths. He is credited for founding the ninja culture and teaching subsequent generations of shinobi how to use all of the shinobi techniques, including chakra mastery. Even though Boruto's introduction of Shibai tsutsuki upset the existing quo, the Sage is nonetheless remembered as a legendary figure who made significant contributions to Earth's advancement.
He was born as Kaguya's son, Hagoromo, which allowed him to control the Ten Tails and become the first jinchūriki, thus that has a lot to do with it as well. However, as Chapter 3 of Naruto: Sasuke's Story -- The Uchiha and the Heavenly Stardust unfolds, fans are now discovering that the Sage had a secret mission in addition to spreading his martial arts across the lands.
Due to His Powers, the Sage of the Six Paths Suffered Illness
In this Heavenly Starudst spinoff, Sakura infiltrates the Redaku base that Sasuke is acting as a spy in, letting him know Naruto's chakra pathways are being blocked due to how he stored Kurama. That's why he's sick, but rather than Sasuke continuing to probe the villainous warden, Zansūru, he should get into town and use the data Kakashi sent. It turns out, the Sage suffered the same disease and came to this region to find a cure.
He couldn't let the outside world know his body was failing him, so he kept it hush. It led him to this facility, where Tataru helped. The man studied the stars, which resulted in the Sage cutting a falling star and using the fragments -- or as the Sage noted in his journals, "heavenly dust." This cured him, so Sasuke now has to find the map the Sage left behind to locate the particles and heal Naruto. This adds sympathy and nuance to the Sage's story, showcasing how he sacrificed by housing the powerful creatures within, and the struggle he had to endure to save himself.
It Feels More Human and Nuanced in The Sage of the Six Paths
Honestly, Heavenly Stardust's story is a breath of fresh air to the tale of the Sage just getting old and dying. Lore does dictate that he passed his knowledge down to his sons, Indra and Asura -- who'd reincarnate as Uchiha Madara and Hashirama -- and then Sasuke and Naruto over the years. It's only until the latter came to be that his vision was attended to, as all he wanted was temples built to effect peace, and for the beasts to be free and happy.
Still, while he had good intentions, the Naruto manga and anime had him as a cold teacher. But this side-mission makes him frail, vulnerable and a lot like the shinobi in Konoha. It leaves fans wondering what other secrets the Sage left behind, what other journeys he made, and if him hiding the dust from the ninja descendants means that Sasuke has to be wary over the particles being a curse, rather than a gift. Either way, it'd be great to get more chapters based on the Sage -- and the friends and enemies he met before and after this illness -- to enrich the character's history.