I mean, I’m just saying, but by definition someone you’ve lived with for over half a year isn’t a stranger. Even if you don’t know everything about them, you’ve interacted with them enough to have some sort of a relationship (and you don’t NEED to know everything about them. I have relatives whose names I couldn’t give, barely know, and met once, still can’t call them strangers). Plus, the cousin has no right to barge in 6 months late and start controlling the MC’s life. First off she should be showing a lot more gratitude to Shiori considering she’s supported and provided for the MC who no one else was around. The MC would be living on his own either struggling, probably mal nutrition, most likely forced to drop out of highschool to get a job, or possibly dead if not for her. Where was his cousin when his parents abandoned him? She really can’t act like his savior, rightful guardian, or whatever when she wasn’t there when he would have needed her (she COULD be more respectful and thankful towards the person providing for and supporting the MC, and then maybe offered for him to live with family again or even moved in closer herself).