|First Lieutenant Tsurumi will scold me!
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Osoma is a rambunctious, highly energetic child who has an affinity for games, particularly the game having to do with shells. She has no shame, as many children lack at her age, and will happily joke with people about disgusting topics such as her own name or say the first thing that pops into her head, such as saying Sugimoto has strange ears when they meet.
Osoma seems to have taken a liking to Genjirou Tanigaki, playing with him often and crying when he had to leave the kotan.
Osoma is first seen when Sugimoto visits Asirpa's kotan. Osoma points at Sugimoto's ears and says sinna kisar. Asirpa explains that Osoma noticed how strange Sugimoto's ears are compared to the Ainu. Sugimoto asks Osoma's name but upon hearing it thinks she is messing with him. Asirpa tells Sugimoto it's not a joke: the Ainu have a custom of giving babies disgusting names to protect them from evil spirits of illness. Once children turn six years old, they get a real name based on their personalities and what they've done in life.
On another day, Osoma and other kids ask Asirpa to play with them. They give her a kisarri ("long-eared monster"), a toy for scaring children which you use while standing outside the window and making scary noises. Asirpa offers Sugimoto to give it a try, but his attempt to scare the children falls flat. Asirpa takes the matters in her hands and shows everyone how it's done, terrifying the children so much that Osoma wets herself. Sugimoto tries again, but fails and kids leave him. Later, Osoma plays with Asirpa in Uko Karip Ciwe, a ring catch game.
That night Osoma falls asleep in Asirpa's cise until Makanakkuru takes her home.
In the kotan, Osoma is playing around with a seypirakka, a shell toy pretending to be a horse, as Tanigaki watches her and comments on how she has been paying with it for several days without getting tired of it already. Wanting him to get in on the fun, she hands the toy over to and instructs him on how to use it. Unfortunately, Tanigaki's heavier weight causes the shell to collapse, injuring his right foot. Osoma hurries off to get Huci as Tanigaki falls over in pain.
Osoma is harvesting plants with her grandmother and Tanigaki for food to eat. Later, they are happily enjoying their food along with her father as Huci smiles at them. Some days later, Osoma is sitting around a fire with her father, grandmother, and Tanigaki. When her father asks Tanigaki what he will do now that his leg has healed, Osoma glances at them with a strange look in her eyes. The next day, a crowd has huddled around a fortune-teller and Osoma along with Tanigaki and Cikapasi goes over to see what the commotion is about. When the fortune-teller, named Inkarmat sees them and mentions looking for a girl with blue eyes, they head back to their hut and listens as Inkarmat says that her cousin might be in terrible danger as one of her companions will betray her.
When Tanigaki makes his resolve to leave the kotan to find Asirpa, Osoma became saddened that she would not see her friend again. At her father's nudging, she gave Tanigaki a hand cover that she made with her grandmother as a farewell gift. She was only able to make one, but she promises Tanigaki that she would have the other one by the time he returns.
- Her name means "doo doo".
- In 2018 Golden Kamuy All-Stars popularity poll, Osoma ranked 29th, gaining 1,433 votes.