Asirpa’s decision to not trust Tsurumi is absolutely the right one. As Shiraishi points out, Tsurumi doesn’t give a damn about the Ainu. The Ainu only served him due to particular interests from the Ainu more so then Tsurumi. In fact, Tsurumi plans to expand with the Gold, so even more bad news. Sugimoto would have lived with regrets if he forced Asirpa into cooperating with Tsurumi, especially when you consider he clearly only views Asirpa as an asset.
Though you really have to credit Sugimoto because it looked like an impossible situation twice. First him getting gunned down where if it were not for Koito’s inexperience it might have been over there. Then with escaping the ferry ice the ice to remain undetected. Though most interesting the actual reason Asirpa doesn’t want to tell Sugimoto about the key regarding the gold because she fears of him leaving him. Considering her father is dead, and her grandmother is getting up there in age. Her willing to go to hell is a bit concerning.
Heita being one of the Tattoo Prisoners is interesting. Though the chapters surrounding him are interesting because there are two elements. The first is these Ainu tales and these are capable of wrecking the mental of someone like Heita if they are told incorrectly. As Heita thought the Wenkamuy killed people as punishment rather than people it likes. Thus, he went into madness imagining the Wenkamuy coming to kill it as he led the bear to kill his parents for taking his gold. The other part is that it also started with Heita gathering gold. Sugimoto does ask a good question is it the gold that drives people mad? Or is it the desire for the gold that drives them mad? It honestly is both because desire of the gold and the opportunities it presents makes men desperate for it. Of course money itself can always drive them mad.