|This article uses material from the Sumaru article on the Naruto wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.|
Like the other ninja of Hoshigakure, Sumaru takes part in star training, a technique which allow incredible chakra control, at the expense of severe physical health damage. He appears to be one of their more prodigious practitioners, being able to perform some of the more advanced techniques of star training at such an early age. Sumaru is told that his parents, Natsuhi and Hotarubi, were killed in battle guarding the fallen star, when in reality, they stole it in an effort to save the villagers from the damaging effects of star training. As a last favour, they asked the Third Hoshikage to lie to Sumaru to protect their family name.
Sumaru remembers his mother, especially, through a lullaby she sang to him as a child about a red star called Natsuhiboshi, which is actually the planet Mars. The lullaby serves as his motivation.
Sumaru was able to use the Mysterious Peacock Method, seen when he was able to create wings made out of chakra to fly and when he could use said wings for an offensive attack. When Akahoshi kidnapped Sumaru, Yotaka said that he was one of the village's most talented genin, indicating that Sumaru had much more control over the Star Chakra like his mother.
He first encounters Naruto at the edge of the Land of Bears where he stops the Konoha genin from walking into a canyon filled with toxic gas, the "Devil's Ravine". Naruto misinterprets Sumaru's actions as an attack, and has a brief, uneventful battle, during which, the Konoha genin witnessed first-hand the Mysterious Peacock Method in battle. When the star is stolen by a mysterious bandit, Akahoshi charges Sumaru and his friends to get it back. Sumaru is taken away by Akahoshi posing as the real mysterious bandit as the other ninja collapse from the side effects of the Star Training.
Akahoshi puts him in "suspended animation," and as Sumaru lays unconscious, he dreams about when the Third Hoshikage tells Sumaru about his parents dying to protect the star, and tells him to be strong and to make his parents proud. Sumaru is rescued by Tenten and Rock Lee. Shortly after, Sumaru is guiding Neji, Tenten, and Lee, with the other Hoshigakure genin, to find the mysterious bandit that stole the star. They all find the bandit, who is actually Sumaru's mother, Natsuhi. Akahoshi uses his jutsu to try to kill him. Akahoshi briefly attacks Natsuhi and wounds her, then Naruto, Neji, Tenten, Lee, and Hokuto, flee to Natsuhi's hideout where Sumaru and Natsuhi rest and recover.
Sumaru awakens, seeing his mother for the first time in ten years. Natsuhi awakens, confessing the reasons why she abandoned Sumaru. He tells Natsuhi to leave him alone, and says that he has these dreams where he cannot catch up with two figures, Sumaru's parents. Sumaru is upset by his mother's abandonment, and says that his mother would never do that. However, he is then in tears and forgives his mother. Sometime later, Sumaru awakens to find his mother's bed barren, and realises what she is about to do: to steal the star to prevent further use. The team of Naruto, Neji, Tenten, Lee, Hokuto, and Sumaru rush to stop Natsuhi, but they are too late; Sumaru's pendant breaks, indicating Natsuhi's death. Sumaru vows to avenge his mother's death, and flies to where Natsuhi's body lays. Akahoshi orders the training hall to be set with flames.
As this is going on, Sumaru realises why his mother abandoned him, and forgives her before the training hall is destroyed. It was revealed that Sumaru survived the blast by his mother's spirit. Sumaru, along with the other Hoshigakure genin, are healed by the Konohagakure medical ninja. Sumaru final vow is that he will become Hoshikage before Naruto, and will make his village the most powerful village that will exceed the Five Great Nations, even without the star's power.