Kiseru Gankubi

is an Outer of Kara.

Background
Kiseru originated from Takigakure, enjoying hot springs with his grandfather. He eventually moved to Konohagakure and became shinobi, where he met Konohamaru Sarutobi. At some point, he secretly also became an Outer of Kara.

Personality
Kiseru is a feisty and determined individual, refusing to give up trying to escape despite making no progress. He is compassionate, readily collaborating with Boruto to help the civilian captives survive Ōga's experiments and urging Boruto to remain positive after some of them died, stressing they did all they could. However, this attitude may be a facade, hiding a working communicator that can help others escape capture.

Appearance
Kiseru is a fairly tall child of tanned complexion. He has dreadlocks reaching his shoulders tied in a ponytail. He also has stern eyes with blue irises and thick brows. He wears a white undershirt, a grey vest, and grey pants with black sandals.

Abilities
Kiseru is able to use Fire Release, able to produce blasts and arrows of fire, or flame-enhanced punches. He can jump several feet in the air quite easily. He has great stamina and pain resistance, attempting to break out of his confinement for quite a while, and being unbothered by his swollen hands after trying to punch his way out. He is also good at improvisation, using the railing of a safe platform to create a ladder.

Labyrinth Game Arc
While on the Thunder Train, Kiseru and all other passengers fell asleep and woke up detained in a secluded room. Kiseru attempted to break out by attacking the walls with Fire Release and taijutsu, with no results. He recognised Boruto, identifying himself as a fellow Konoha-nin. Ōga revealed himself as their captor, and announced he'd put them through experiments to test their ability to avoid death, putting them through five tests before they can leave his maze. After the "Collapse" test was chosen, the group was teleported to atop of a brittle stone floor floating above a massive chasm, requiring them to reach a safe platform. He and other shinobi attempted to attack Ōga, who turned out to be a projection. Concerned by the others still on the platform, Kiseru grabbed one of the rope barriers and lowered it as a makeshift ladder for them to climb. He was sad they couldn't save everyone, but assured Boruto that they did the best they could.

While waiting for the next experiment, Rokuro attacked a Kusa-nin, accusing him of being Ōga's minion. Kiseru recognised the merit in the accusation, recalling how he had pushed him when Kiseru was near him at edge of the falling platform before it began crumbling. He died from Rokuro's jutsu asking for Ōga's help. Ōga arrived and sent them into the next experiment, which involved candles connected to their lives. When the group who decided to work together came across a closed gate, Kiseru and Namua trusted someone else to hold the lanterns with their candles to help Boruto force it open. In the next room, he along the other shinobi helped protect the non-shinobi from a dust storm while they protected the entire group's candles, and informed Boruto that Shamo had gone ahead with a woman he liked. Near the end, they had to take a slow-moving elevator, and realised that their candles wouldn't last the entire ascent, Ōga intending them to steal each other's candles. Boruto exploited the exact wording of Ōga's rules to make one long candle with the remains of everyone else's, shared by all, so they all survived the ride, clearing the experiment.

While waiting for the next experiment, Kiseru told everyone his goal of going to the hot springs his grandfather used to take him to if he escaped the maze. When Ōga returned to begin the next experiment, Kiseru selected the "Collapse" test. The group was teleported to another room, where soon the wall began to fall on them. When discovering only a few chambers for people to squeeze into to escape being crushed, Kiseru fought Rokuro for one, but was quickly overpowered as his flame attacks were repelled. As Boruto put out the flames with Water Release, he discovered that the floors weren't completely solid as the water seeped through. Kiseru helped Boruto to break through the floor. Ultimately, Batta was convinced to help and was able to find the weak point in the floor, letting Boruto break through to save everyone. With the test cleared, everyone was returned to the original room. Batta bumped into Kiseru and secretly stole his communicator, learning of Kiseru's secret nature.

Trivia

 * Written as 煙管, "kiseru" is a type of Japanese smoking pipe, while his surname indicates the shank of the kiseru.