Ōga

is an elderly man who kidnaps people for his survival experiments.

Background
Ōga began abducting many people for his experiments. Eventually, his actions prompted the Five Great Countries' Joint Investigation Team to investigate. The team suspects he is a remnant of Kara.

Personality
Ōga is an eccentric if not deranged old man. Amoral, he is so fascinated by the concept of life and death, of how people are able to escape death, he has no qualms about putting people in peril just to see how they will react and likewise will kill people just as randomly. He has no regards for his subordinates, unbothered by their deaths if they fail him. In his pursuit of researching survival instincts, he is shown to be very elaborate and methodical in his experiments.

Appearance
Ōga is a short, elderly man of heavily wrinkled, light complexion. He has a wide smile with several missing upper teeth, pupilless green eyes, scraggy white hair reaching his lower back with a long white beard. He wears brown cloths and a red cap with a yellow tongue and white wings on the side.

Abilities
Ōga is a skilled puppeteer, able to manipulate one disguised as himself from a far. He can use the Yin Release to project himself in front of people. His genjutsu can also produce elaborate stages to fool his targets. He also is skilled in fūinjutsu and space–time ninjutsu, having set up several scrolls to warp people to new locations.

Labyrinth Game Arc
When several passengers on a Thunder Train wake up secluded in a room, Ōga introduced himself through a puppet of himself, claiming that they survived an accident and were exposed to a toxic gas. Ōga believed they had a subconscious ability to avoid death, and wished to test it. When one of the captives drew a death card, he killed them, stabbing them though their head with a puppet. Boruto attacked the puppet with Wind Release. Having made clear how serious his tests were, the first of five experiments began when a Kusa-nin angrily knocked over one of the scrolls, he accidentally activated the "Collapse" test, sending everyone to new location atop of a floor that hovered over a large chasm. Ōga explained that sections of the floor would quickly crumble away and they needed to escape to a higher, safe ledge. At the end of it, only 14 captives survived, and he congratulated them, allowing them to return and rest before the next test.

When Rokuro deduced that the Kusa-nin was actually Ōga's underling, he forced him into confessing it, resulting in his death. Ōga confirmed it indifferently when he announced the next experiment, Rokuro picking the "Light" test. The captives were presented with candles, and he explained the flames symbolised their lives, them dying if the flames went out. After providing them with lanterns to keep them and explaining how they could be passed around, he sent them off. At the end of the experiment, he intended them to try stealing each other's candles during a time-consuming portion. While the group containing self-centred people resorted to stealing others' candles, Boruto's group where they cooperated, exploited the wording of his rules to create a longer, communal candle, resulting in no deaths in that group. He was impressed by their ingenuity.

For the next experiment, "Pressure" was selected, which he found the harshest yet. It involved everyone trying to get into a limited number of alcoves to avoid the rooms' hazards, including a descending, spiked ceiling. However, the group discovered there was a hidden space under the floor, and they were able to use it to avoid being crushed. Ōga congratulated Boruto, as everyone surviving it would allow him to make the following experiments more interesting. Ōga complained that Boruto and Batta were late for the selection of the next experiment, "Calculation", and explained how they had to reach a gate within a two-hour limit after getting enough cards to sum 7, from cards numbering 1 to 8.

It was later learned that the captured people were in fact contain in capsules in a state of suspended animation, experiencing the various tests inside an elaborate genjutsu.