Another issue, this time with psychology. The girl is too trusting.
1. He's Japanese, she's Ainu, there should be some distrust.
2. He's a strong man, she's a young girl. As a person who understands how to take care of herself, she should be much more careful. She's not a spoiled child from a city who has been protected by her parents all her life. And the times are dangerous...
3. He's a soldier who killed people. It won't be an ethical issue for him to kill her. Isn't it another good reason not to trust him?