Seele flashed a very "sane" smile and said to the grimacing Sin:
"Look at how scared you are. It's so adorable~"
"You... you're not Seele! Who the hell are you?!" Sin yelled at her. This person was definitely not Seele. Seele would never wear such a sick expression.
Unfortunately, Sin's words seemed to have angered her. Her smile gradually stiffened.
"How rude. It seems your impolite mouth needs to be taught a lesson."
Seele pinched Sin's cheeks, forcing her mouth open. Then, with a wave of her hand, a shadow shot directly into Sin's oral cavity, churning violently inside.
"Ahhhhh—" Sin screamed in agony, snot and tears streaming down her face, saliva mixed with blood flowing everywhere. Her teeth were forcibly ripped out by the shadow.
Seele held up the teeth, brandishing them triumphantly in front of Sin. She relished tormenting others. Sin's agonized expression excited Seele to no end, and she couldn't stop laughing, not even noticing the drool trickling from her own mouth.
"What a loud noise... but, how delightful to listen to! Ahaha~"
Seele turned sideways, revealing the symbol of the strong, and looked at Sin with a sidelong glance. But then, as if remembering something, she reined in her smile slightly.
"Oh my, I was just so happy to see you, Sister Sin, that I almost forgot Seele was here to get revenge for my dear sister~"
Seele grabbed Sin's head and dragged her into the room. Then she looked at her with a delighted expression.
Facing the bewildered Sin, Seele laughed and shouted.
"Come on! Let's revel in madness together! Let's call it[The Revenge Play of the Staircase]!! Ahahaha—"
Then, Seele activated the Stigmata on her chest, and amid her own crazed laughter, she dragged Sin's consciousness into the Stigmata Space. Sin's eyes lost their light, and her body collapsed to the floor like a corpse.
When Sin came to, she found herself in a bizarre space. There was nothing but the staircase beneath her feet.
"Where is this? What the hell is going on! You bastard, where did you take Seele?!"
"This is your retribution~ Your retribution for pushing Sister Bronya down the stairs."
Sin followed the voice and saw a colossal Seele, resting her face on her hand, smiling down at her. Her crimson eyes were particularly striking in this dim space.
Seele stretched out a hand and pushed the stunned Sin down the stairs. This was the suffering Sister Bronya had endured, and Sin had to experience it in turn. But the merciful Seele didn't want to hurt Sin, so the kind Seele pulled Sin into a space of consciousness. Quick, say thank you, Seele.
Again and again, Sin tumbled down the stairs, which seemed to have no end. Sin didn't know how long she had been falling, until she was on the verge of losing consciousness.
"Heh heh..."
With a cold laugh from Seele, the stairs suddenly ended, but there was nothing below. Sin grabbed onto the last step, hanging in the air.
"Save me..."
"Coming~" Seele shrank to a normal size and slowly walked towards Sin, a giant scythe in her hand. "Don't get the wrong idea, I'm not here to save you~"
She stepped on Sin's hand, leaving her dangling in the air, then swung the scythe, hacking at Sin's body again and again.
"You won't be spared any of the suffering Bronya went through~"
After an unknown amount of time, Sin's screams gradually faded.
Back in reality, Seele sat on a couch constructed from her Honkai energy, looking at the unconscious Sin lying on the floor, having lost control of her bodily functions.
"So useless. You were so full of bravado when you were the one doing the bullying.
Right, what's this paper she kept looking at? Hmm?"
Seele picked up the list Sin had been staring at. Her red eyes were instantly overcome by blue.
"...Is this?!"
Sometime later, in Cocolia's office.
Cocolia was still working when Seele knocked and entered.
"Seele?! It's so late, why aren't you asleep?"
"Mama... please tell me, what exactly is the X-10 experiment!"
"Hmm? Did that Bronya girl let it slip... Well, you all would have found out sooner or later."
Cocolia paused for a moment, then stood up from her chair and walked over to Seele, beginning to explain the X-10 experiment to her.
"You should know that the Honkai energy that overflows during a Honkai eruption erodes normal human bodies. But children like you, who have an immunity, can resist the Honkai energy's corrosion and even control it to some extent.
But the immunity's protective effect is limited. In the end, your bodies will still be destroyed by the ever-changing Honkai energy.
Therefore, the X-10 experiment was proposed. The goal of this experiment is to find a way for the body to completely adapt to the Honkai.
If the experiment succeeds, you children will become a new type of human, able to survive in the Honkai."
"But what if the experiment fails? What will happen? Will Sister Bronya... die?"
Cocolia placed a hand on Seele's shoulder, comforting the agitated girl.
"Bronya has a very high adaptability to Honkai energy. Even if she fails, her data can help us further understand it. Do you understand?
That way, we can save the others. Bronya... she volunteered for this experiment so that you could live..."
"...I understand, Mama." Seele lowered her head, looking towards the spot where her Stigmata was. She pulled open her shirt, revealing the Stigmata on her chest. In that moment, Seele began to actively release Honkai energy.
"Warning, warning— Warning, warning—"
As the Honkai energy alarms blared, Seele spoke.
"In that case, Mama, there is someone even more suitable for this experiment."
"To be able to control such powerful Honkai energy!! Could this be the legendary Stigmata?!"
"Mama... Please let Seele... take Sister Bronya's place!"
Cocolia was silent for a long time, but in the end, she agreed.
Perhaps this was fate. Cocolia didn't want Seele to participate in the experiment, but possessing a Stigmata made her the best possible test subject.
"Go say goodbye to Bronya. Don't leave any regrets..."
Seele nodded and left. She would go see Sister Bronya.
Seele stood at the door to their room for a long time, but ultimately couldn't muster the courage to speak to Bronya. She left the experiment notice outside the door and departed.
Seele wanted Bronya to know, yet she was afraid Bronya would stop her. If Bronya asked her to stay, Seele knew she would definitely hesitate.
So she had Cocolia prepare a transport aircraft overnight, and the two of them set off for the research facility before dawn.