I love Owari no seraph novel, but there are things that i really hate.
This part:  “don’t tell me you intend to murder someone here? ” Mahiru to Seishirou.

 Seriously?
You killed a lot of people for your own goals and you say that?

This part: here your attendant! To Guren , come on!! . “I hate getting apologies from you. Especially, from the you who is always weak and cannot protect a girl”.

Who do you think you are? You didn’t help her because you wanted be nice with her, you treated her like a servant and you helped her because Guren was there, and the worst part is that you offend, selfish.
In the novel Mahiru decided to go meet Guren because Tenri killed her mother, from the start she knew who was Guren, so yeah she uses Guren. Again selfish.

Ok now this part It makes me angry.

In the competition held once every year, where killing each other was allowed, you were disposed if you didn’t win.
If you don’t win, you die.
If you don’t win, you die.
If you don’t win, you die.
Moreover, one and only one person can survive.
He no longer rememberd how many people were there at the start.
He just desperately tried every day.
To learn new sorcery spells (jujutsu).
To learn new illusion spells (genjutsu).
To obtain new physical abilities (taijutsu).
Once every now and then, he befriended someone. A friend to celebrate their survival together.
But that friend got disposed for not being in the top 30%.
That instilled fear in everyone, and they all put in more effort than ever.
Met a friend.
That friend died.
Met a friend.
That friend died.
He stopped befriending others. (ALL THIS IS SO SAD) Poor Shinya, he doesn’t deserve all this bullshit.

To what the instructor said, Shinya replied while smiling.
“Then, I don’t have to compete anymore?”
“Yes”
“I survived?”
“Yes”
“Ah. I did…”it.

Well now, what the hell is this?

“I do not hold any interest in you, so just be yourself.” “I already have a person I love. Therefore, I cannot accept you. Today, I came to tell you this.” Mahiru to Shinya.

You watched all the fight, you saw how these kids were forced to kill each other for you and you didn’t care and you acting like a bitch? How can you be so selfish?

“Ahaha. I wish I was born a normal child.”
“……”
“In a house, that would allow me to love whoever I loved.”
That - wishing to be born as a normal child -  was the same for Shinya himself.
Kill others to survive.
Get disposed if you fail to produce a quality result.
He did not want to live while fighting against such fears

.
Seriously ? What a selfish girl, he survived to a hell and you just care about you?
And this:

Upon Shinya’s words, Mahiru laughed again.
A bright smile resembling of this calm, serene afternoon.
“Guren is strong, probably. Stronger than me. A lot.”
“So, you like that Guren person?”
“Mhmm.”
“Because he’s strong?”
“Mhmm.”

So what, do you love Guren or just to want use him?  These words are suspect; you planned this from the beginning, it’s what I believe.
Mahiru is selfish, possessive & super manipulative, she does not care about anyone but herself, and I’m tired of demonic possession, it’s just an excuse, because she wasn’t possessed here and she acting like a bitch.
She just uses Guren, and sometimes I think how Guren can be so idiot, I mean I love him he is so kind and selfless and this woman just destroyed him , she is a typical Hiragi to me, is like Kureto, Seishirou and Tenri. The Hiragis use Guren now and always