The Culprit Behind

                                    

                                          
Bismarck personally inspects salvaged Siren parts from a recent battle. In one of the spacious warehouse of the base, she has it suspended in the air by chains. She analyzes the surprising intact section of a rigging as she walks around it and slowly moves her head.
"How about that one?"
There's nothing particular unusual from the object other than the section has been blown off from the mass-produced humanoid Siren. What she's more intrigued is the salvaged barrel from a Siren Tracer displayed on top of a long wooden table.
"It's from another fleet. The way it was destroyed was strange, so we had to bring it" Mainz walks towards the table
"It's still freezing....."
Bismarck approaches it and keeps at least a few inches of distance from the table. The barrel has been severed not from a blast or a clean slice, but the section breaking off from the rest. The metal had become fragile that it shatters on its own leaving it like snapping off a branch from the rest of the tree.
"This isn't Tirpitz's power...." Bismarck whispers to herself
Faint cold air still evaporates from the broken part, mostly visible from the end where it was broken. Oddly enough, even when Bismarck gently rubs the center with her fingertips, it doesn't shatter or even crack.
"What do you think did this?" Graf Zeppelin approaches from the right
"Someone attacked the Sirens and left nothing but scraps. It's either they had an inevitable encounter or someone used them as target practice"
Bismarck turns her head to more parts lying on top of the table. Unlike the barrel, the parts show cracks but not enough to crush them into bits. The rigging is either highly resistant or the perpetrator controls the amount of power.
"Has the Wolfpack found evidence that it was from an aircraft carrier?" Bismarck looks at Mainz standing at her left side
"Unfortunately, no. A sudden blizzard hindered them as soon as they entered the battlefield. By the time the weather calmed down, the attacker disappeared and left the frozen Siren debris" Mainz shakes her head
"However, they were certain they at least detected two kansens. One of them was a destroyer" Graf Zeppelin adds more information
"They couldn't detect the other one?" Bismarck raises an eyebrow
"An unknown wave distorted the other ship's presence. They described it as something that swept their faces on the way there. It's a jamming device, but we were countered when the culprit detected our group first" Graf Zeppelin speculates
The only one Bismarck knows who had such an ability to control extreme temperature is either her younger sister or the unknown kansen who she believes is Victorious. Neither of the two are near Iron Blood territory as Tirpitz is taking her time off back in the Mediterranean and Victorious is away on a mission at the Pacific.
"......!" Bismarck suddenly jolts
When Bismarck suddenly takes a step back, the two kansens with her nearly widens their eyes in surprise. Bismarck reflexively grabs the back of her neck feeling a threat looming behind her. It's her instinct to protect herself, but there's no visible threat around her, just two silently confused subordinates.
"What's the matter?" Graf Zeppelin first shows concern
"Nothing. It felt like I was being watched......" Bismarck rubs her left shoulder
There's no one behind Bismarck as she quickly turns around. The only thing present is the quiet breeze and dust within the warehouse. She keeps turning her head left and right, but this only worries the two because Bismarck remains alert with no enemies present.
"Strange. I really did feel someone was looking here" Bismarck shakes her head
Shortly after, she brushes off the sudden nervousness that rushes to her spine. It's no different from walking alone with the constant anxiety of being stalked by an invisible force. It's the unshakable vulnerability of all living beings since the beginning. The fear of being exposed to an intangible threat. Even someone as strong-willed and resilient as Bismarck is no exception to this.