|First Lieutenant Tsurumi will scold me!
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Rikimatsu Ariko (有古 力松, Ariko Rikimatsu), or Ipopte (イポㇷ゚テ, Ipopte), is an Ainu man and a Private First Class of the 7th Division.
Ariko is a very muscular man with a dark complexion and long black hair tied back in a bun, a tuft of beard on his chin as well as chest hair that stretches all the way down to his groin. He has large eyebrows that often gave him a very stern look, but his most defining feature is a scar that stretches from the bottom left of his face all the way up to the right side of his head that is closed together with five stitches. As a member of the 7th Division, Ariko wears the Imperial Japanese Army uniform.
As a child, Ariko was rather pudgy with a stout nose, thick lips, and just a small patch of hair on his bald head.
Ariko is knowledgeable in some of the Ainu customs, such as knowing where secret hot springs are located and being able to instantly recognize Ainu clothing.
Ariko was born in Hokkaido, near Noboribetsu. As a boy, Ariko entered a mine in Penkeyu during wintertime and explored it enough to find several exits within.
He was one of the members of the search and rescue groups on Mount Hakkoda where they helped to rescue members of the 5th Infantry Regiment that had gotten lost on the mountains.
Ariko was relaxing in a secret hot spring when he met a strange man who was running across the snowy mountain wearing geta and with no light on at all. Afterwards, he told of this encounter to several members of the 7th Division, including Warrant Officer Kikuta.
As Kikuta told of the encounter to Private First Class Kouhei Nikaidou and Superior Private Usami, Ariko approaches them and explains more of the story, saying that even though he heard the sound of geta, the tracks left behind in the snow were from straw boots. He goes on to say that the strange man's clothes had gotten his attention since they had an odd pattern on them, but he was unable to make them out. Nikaidou and Usami does not believe him with the former saying that their minds must've gotten soft since they had been relaxing in Noboribetsu since the war ended, and the latter playfully scolding him for his harsh words.
Once they had finished bathing and got dressed, Nikaidou asks why Ariko was at a hot spring so deep in the mountains and Ariko says that there is a secret hot spring that only the Ainu knew of, revealing himself to be an Ainu much to Nikaidou's surprise. Usami wonders if the strange man might have been an Ainu as well since their clothes have odd patterns but Ariko says that he would have recognized the strange man's clothing. Kikuta says that he found the story intriguing but laments that he may have been overthinking it, asking the anma massaging him if he knew anything. The anma replies that if he saw some clothes with a strange Ainu pattern, he would be sure to let them know.
Sometime later, Ariko meets with Kikuta and he tells him to go back to his village and ask around if anyone else has seen the strange man as well. As a couple of other soldiers walk by, talking about a pretty girl, Ariko confirms his objective and Kikuta laments that they are falling behind Usami and that they should get a gift for First Lieutenant Tsurumi if they wish to work alongside him again. Afterwards, Ariko returns to his village and meets the elder, asking about the man with strange Ainu pattern clothing but she tells him that they are not Ainu patterns but tattoos, which surprises Ariko.
As Ariko leaves his village, he hears a couple of gunshots and wonders if they were coming from the direction of the Hell Valley. He takes out his rifle and runs towards the Hell Valley to find Kikuta fending off a couple of attackers, confirming to him that what he saw was a tattoo. Upon hearing this, Kikuta tells Ariko and Usami to come with him to chase after the lone man who had escaped the fight. As they look for their foe within the woods, Kikuta realizes that the strange man was actually a tattooed convict and Usami admits that he knew all along. Hearing this, Ariko wonders why a tattooed convict would put himself in so much danger just to hide out at a hot spring resort used by the 7th Division.
The three soldiers spot the convict running away from them and Ariko shoots at him but barely misses as he hits the tree instead. They follow his footprints to a mine which Ariko states that he had been inside before as a kid. Kikuta asks if there are other exits inside and Ariko confirms that there are, if they haven't already collapsed. They hear the convict's clicking sound from within and Kikuta warns them not to light a match and to be quiet. However, Usami knocks over an ice stalagmite, causing the convict to shoot at them and injures Usami. The three of them realizes that they are at a major disadvantage as one false move could give away their position.
As he remains cautious, Ariko notes that he had entered the mines once before but never paid any attention to the ice and if they had a cinoyetet torch, they could have avoided the ice surrounding them. Just then, he knocks over an ice stalagmite with his rifle and manages to react quickly enough to avoid the convict's gunfires. As Kikuta and Usami fires back at him, Kikuta notices something odd about the way the convict is moving and so creates a torch to reveal that their opponent was the anma from the hot spring.
They chase the anma out of the cave and hears him clicking nearby but Usami limps out of the mines, asking Kikuta not to leave him behind. Kikuta turns to Ariko and tells him not to let the anma get away and Ariko swears not to. Afterwards, Ariko follows the anma by himself, breaking the tree branches around him in order to lead the anma into a trap. Ariko takes his rifle out and fires at several points around the anma so that they would cause an avalanche to occur and engulf the anma in the heavy snow, killing him.
Ariko digs out the corpse from under the snow and examines the convict's tattoo, realizing that it was meant to be skinned like an animal. He knew that Kikuta would ask him to obtain the anma's gun and so attempts to look for it but was unable to find it buried under all the snow. Ariko also expects that Usami may try to steal their glory from them so he decides to wait in his Ainu village until Kikuta finds him. Four days later, an eldery Ainu woman approaches Ariko to present Kikuta who playfully scolds him for not telling him that he is still alive, and Ariko apologizes for keeping him waiting. Ariko shows Kikuta the anma's tattoo and explains the reasons for all of his actions since fighting the anma and Kikuta praises him for his decisions making and that they now have the best possible present for Tsurumi.
- Ariko likes hazel grouse but dislikes shark.
- Ariko is shorter than Ushiyama, same height as Tanigaki, and taller than Kiroranke.
- Since Ariko is as tall as Tanigaki, it's safe to assume that his height is 185 cm (6'0), too. 
- Ariko is lighter than Sofia and Tanigaki, and heavier than Kiroranke.
- His Ainu name Ipopte means “to bring to a boil” (to become hot in an instant).
- Ariko is the same age as Tanigaki.
- According to Satoru Noda, Ariko has one of the "juiciest" asses in the manga; the other listed characters are Tanigaki, Tsukishima, Shiraishi, and Usami. 
|7th Division Members||Hajime Tsukishima • Kazuo Maeyama † • Kennosuke Mishima † • Kouhei Nikaidou † • Mokutarou Kikuta † • Otonoshin Koito • Tokishige Usami † • Tokushirou Tsurumi • Youhei Nikaidou †|
|Deserters||Fumio Okada † • Genjirou Tanigaki • Houzou Tamai † • Hyakunosuke Ogata • Ikutarou Komiya * • Naoaki Noma † • Rikimatsu Ariko|
|Allies||Heiji Koito • Hidenobu Okuda • Narizou Arisaka • Teruchika Yodogawa • Yasaku Edogai †|
|Associates||Kouji Wada † • Koujirou Hanazawa † • Yuusaku Hanazawa †|
|Main Group||Kantarou Okuyama • Kirawus • Rikimatsu Ariko • Shinpachi Nagakura • Tatsuma Ushiyama • Toshiyuki Kadokura • Toshizou Hijikata|
|Former Members||Anji Toni † • Hyakunosuke Ogata • Kamezou † • Kano Ienaga †|
|Associates||Kenzou Tamoto • Kiroranke † • Takuboku Ishikawa • Yoshitake Shiraishi|