Chapter Text
Using the device that monitors his vitals, Dazai can vary his heart rate at will and digitize his messages in order to communicate to the outside world, which Ango then uses his government access to retrieve and decode.
Dazai has trained himself to perfectly regulate his heartbeat. He can make it slow, steady, even fake bradycardia or tachycardia at will. It’s how he bluffs his way through interrogations, danger, lies… basically, he’s unreadable.
Except… Chuuya.
Something about Chuuya just slips past the control. Maybe it’s the irritation, maybe it’s adrenaline, maybe something deeper he’s not ready to face, but every time Chuuya’s near, Dazai’s pulse spikes and he knows it.
And because they still partner occasionally, this happens a lot.
After several successful uses of the device, it was repurposed into a watch, which Ango wears when needed, especially during important missions.
The device monitoring Dazai's vitals tells his physical state, stress level, lies, etc… all from subtle variations.
Meaning every time Dazai acts like his usual smug, unflappable self around Chuuya…
Ango knows it's all an act.
And the worst part of it all is that Ango never says it outright. He just raises an eyebrow in a way that makes Dazai paranoid like what the hell does he know?
***
Chuuya’s yelling at him mid-battle, and Dazai’s desperately trying to keep his heart rate even, but he’s dodging bullets, Chuuya’s coat is flaring dramatically, there’s blood on his cheek.
Dazai’s heart skips a beat and he feels it.
In the comms, Ango’s quiet voice: “You okay, Dazai?” in that tone.
Dazai doesn't show it, but forces his heartbeat to slow down.
After the mission they gather at a bar. Chuuya storms off. Dazai’s pretending not to care, spinning his glass lazily.
Ango, sipping his drink, remarks, “…It’s fast again.”
“…Shut up.” He receives in response.
***
Ango and Chuuya both in the same room, talking about something, while Dazai’s stuck nearby. He’s controlling his breathing, focusing on his pulse.
And then Chuuya laughs at something Ango says.
Dazai’s heartbeat jumps.
Ango just smiles faintly without looking at him. Dazai knows he noticed.
***
Post-mission debrief, a small conference room.
Chuuya’s pacing, still in battle gear, hair mussed from wind and gunfire. Dazai’s sitting cross-legged on the table like nothing happened. Ango’s typing notes on the side.
An argument ensues about how Dazai decided to arbitrarily change the plan without informing Chuuya in advance. Dazai justifies himself by saying that he decided to change the plan during the mission, and that everything ended well, so there’s no point in picking on him now. He smirks, resting his chin in his hand. Cool, steady, calm.
…Until Chuuya steps closer. Close enough that the faint smell of smoke and rain clings to him.
“You almost got us both killed, you jackass!” He snaps, grabbing Dazai by the collar.
His heartbeat spikes, just a fraction, before he forces it back down.
From the corner, Ango doesn’t look up from his laptop. “…Eighty-four beats per minute.”
Dazai freezes. Chuuya frowns, letting go of his collar. “What?”
“Nothing.” Dazai intervenes.
“It was sixty-three a moment ago.” Ango continues.
Chuuya’s glaring between them. “What the hell are you two talking about?”
“Nothing important.” Dazai shrugs with a smile.
“He’s lying.” Ango says, still staring at the laptop screen.
Dazai slouches, muttering under his breath. He can feel Chuuya’s eyes on him and, annoyingly, his pulse jumps again.
Ango just sips his coffee without looking up, the faintest smirk tugging at his lips.