The issue is everybody else is not freaked out by this.
This demon literally said to your face she killed hundreds of people and nobody bats an eye? What the actual fuck?
Why has no ome sealed her back yesterday?
If two persons come up to you and one says "I like My Little Pony" while the other say "I like to murder people for fun" it's the same?
Makoto only just seems to have even accepted that she's even the actual demon she says she is. For the first chapter and first half of the second, he kept referring to her as a cosplayer, and even now just calls her a weirdo.
She's also a known entity in terms of the mythology of the town they live in, going back centuries' worth of time, and the lore surrounding her being is well-established, right down to the significance of the Mike bloodline.
Touri's own bloodline is directly responsible for exorcising/otherwise controlling the demon princess. She's been raised within that mindset, clearly, given how immediately she jumps to wanting to protect Makoto from Orihime. (The reason she isn't successful, is because she's a novice with no 'real world experience' dealing with supernatural entities, as Orihime was sealed for centuries up to this point anyway.)
We see her own grandmother treat Orihime with veneration and offer her food and hospitality. I'm not supremely knowledgeable about historical Japanese customs when it comes to spirits and deity worship, but they
do care a lot about the concept of respect toward those seen as 'higher beings', including their deceased and the multitudes of kami and other spiritual entities that Shinto is based around. Even a demonic being who demanded sacrifice would be worthy of worship and respect, as we're told that Orihime
did also prevent and divert disasters in the past that were wrought by other supernatural forces. That alone shows she's not simply a murderous being.
And very importantly - Makoto himself has given up on his life and is convinced that it doesn't matter, because he'll never be happy enough anyway for his life to be in danger as a Mike. He simply doesn't care in the wake of the tragedy he's faced.
Orihime's a deity-like being. Yes, she ate the Mike line as part of the process of maintaining her power, but we have already seen it's more complicated than that. She's also greatly weakened by virtue of having been sealed for so long, so she doesn't presently pose much of a threat, and is more of an annoying freeloader than powerful demonic entity. She has proclaimed to protect and nurture Makoto until his lot in life improves, and even seems intent on pushing him and Touri together, which apparently would benefit
Touri, seemingly smitten with Makoto as she is.
Like....yeah. This is dealing with a demon princess as the female lead of a love story. If anything, I'm glad the author's making her relatistic in terms of what she would actually be as a mythological figure within the story, and the inherent tension of her wanting to
eat the male lead means that the story has something to push against as the characters clash and grow through the experiences they undergo.
We definitely have justification for why she's not being immediately exorcised here and now, though, so if it's that objectionable, I simply think it's going to not be an enjoyable read for anyone who can't let go of that angle of the plot.