I threw this together quickly so expect me to expand it. This is more like a prelude.
Cutlery was placed upon a chabudai. Located in a rather dull room with white walls, black ceiling and a stiff gray rubber-like floor. Towards the corner of this room was a matress, pillow and blanket. Further furnishing being promised if the contained was cooperative with regular questioning and testing.
A dish of breakfast had been made for the one who lived here. And as per agreement she was to be questioned. Perhaps the meal was for encouragement, they knew she could not die conventionally away.
It wasn't unusual for the food to include toxins or other unseen, almost magical qualities. Fujiwara no Mokou had witnessed these different scenarios over the past five days. How she arrived and why she stayed was a bit of a story, none she felt encouraged enough to tell.
"SCP-3561, we would like you to participate in a questioning in exchange for food that you've requested. Do you accept?" One of the men talked to her in Japanese over the speakers.
Fujiwara no Mokou looked at the D-class in front of her, who looked nervous. Her voice cut through the awkward silence, speaking just a little old fashioned. "I'll if I think it's appropriate, as long as you don't poison me today. I can't die, but it can still hurt things in my body."
"I see-" The voice then cuts into a language foreign to the immortal, though she'd heard of such being spoken at the Misty Lake's mansion before. "Begin recording."
"You call yourself Fujiwara no Mokou, our research has linked you to an old Japanese clan, though previous questioning hasn't yielded results. Why is it that you have become immortal and maintained life to this year?" The Japanese voice asked. In the background, foreign words about clearance and redaction could be heard, but aside from what very little she'd picked up on from these researchers, she didn't know much of the foreign language.
"That's a story far greater than the one of my arrival here. I'm not sure if I'd like to tell it. And I've answered the first question before, I'm an ordinary health maniac who runs a yakitori stand." She replied bluntly.
"Next question. You've displayed a manner of weird abilities since you were captured, predominantly featuring flight. Do you understand how you achieve this?"
"Yeah, I do. It's quite difficult to learn it as a human." The immortal replied nonchalantly. Even if today was just a questioning, she was going to use it for her entertainment. Using delicious and strangely poisoned food for testing on her hadn't pleased her, and she thought they were irritating. Although, they paled in comparison to the princess in that regard.
The sound of the containment gate opening was suddenly heard. And not long after, the door to her room opened as well. The immortal looked surprised, but excited by this new development. A smile subtly appearing on her face.
Another person spoke through the speaker as commotion started outside. The scientist spoke back in the same foreign language as the lights suddenly went out momentarily. With a blink, they were back on. A shiver washed over her back as the facility shook, she heard a roar somewhere and much worse. But none of this would outright terrify her.
"SCP-3561. We're aborting this questioning. If you have any intention of staying on the foundation's good side, it's best you remain in containment until the breach is solved." The speaker rang out one final time before going silent along with a set of footsteps. There was the sound of a firearm, much sharper in sound than the ones found in Gensokyo. Then there was nothing, the alarms stopped and total silence enveloped the entire site.
Mokou stood up and took the dish with the plate with her. Fueled by her very recent love-hate relationship with this mysterious organization, she left the containment chamber, her long silver hair beautifully dragging across the floor as she did. She wasn't sure what she was in search for. Food? Gensokyo? Other creatures and people of the supernatural?